U.S. patent number 8,083,906 [Application Number 12/849,236] was granted by the patent office on 2011-12-27 for processing biomass.
This patent grant is currently assigned to Xyleco, Inc.. Invention is credited to Marshall Medoff.
United States Patent |
8,083,906 |
Medoff |
December 27, 2011 |
Processing biomass
Abstract
Biomass (e.g., plant biomass, animal biomass, and municipal
waste biomass) is processed to produce useful products, such as
fuels. For example, systems can use feedstock materials, such as
cellulosic and/or lignocellulosic materials and/or starchy or
sugary materials, to produce ethanol and/or butanol, e.g., by
fermentation.
Inventors: |
Medoff; Marshall (Brookline,
MA) |
Assignee: |
Xyleco, Inc. (Woburn,
MA)
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Family
ID: |
41319250 |
Appl.
No.: |
12/849,236 |
Filed: |
August 3, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100304439 A1 |
Dec 2, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12417880 |
Apr 3, 2009 |
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Current U.S.
Class: |
204/157.63;
204/157.15 |
Current CPC
Class: |
C12P
7/06 (20130101); C12P 5/02 (20130101); C08J
3/28 (20130101); C12P 7/10 (20130101); C12P
7/16 (20130101); C08H 8/00 (20130101); C08J
2397/02 (20130101); Y02E 50/10 (20130101); C12P
2203/00 (20130101); C12P 2201/00 (20130101); Y02E
50/30 (20130101) |
Current International
Class: |
B01J
19/08 (20060101); C07C 1/20 (20060101) |
Field of
Search: |
;204/157.3,157.63,157.15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hendricks; Keith
Assistant Examiner: Raphael; Colleen M
Attorney, Agent or Firm: Leber Patent Law P.C. Leber; Celia
H.
Parent Case Text
RELATED APPLICATIONS
This application is a divisional of pending U.S. Ser. No.
12/417,880, filed Apr. 3, 2009, the entire content of which is
incorporated by reference herein.
Claims
What is claimed is:
1. A method comprising: providing a biomass feedstock that has been
irradiated with electron beam radiation such that the biomass
feedstock is ionized and has a first level of radicals; and then
quenching the biomass feedstock, to an extent that the quenched
biomass feedstock has a second level of radicals lower than the
first level, by contacting the biomass with a gas capable of
reacting with the radicals, wherein the level of radicals is
measured in a solid state.
2. The method of claim 1 further comprising preparing the biomass
feedstock by reducing one or more dimensions of individual pieces
of the biomass feedstock.
3. The method of claim 2, wherein reducing one or more dimensions
of individual pieces of biomass feedstock comprises shearing,
grinding, cutting or a combination of these methods.
4. The method of claim 1 wherein quenching comprises quenching the
radicals to such an extent that the second level of radicals is not
detectable with an electron spin resonance spectrometer.
5. The method of claim 1 wherein the second level of radicals is
less than about 10.sup.14 spins.
6. The method of claim 1, wherein the method further comprises
treating the biomass feedstock with one or more other pretreatment
methods, wherein the other pretreatment methods are selected from
sonication, pyrolysis, and oxidation.
7. The method of claim 1, wherein the electron beam radiation is
applied at a total dosage of between about 10 MRad and about 50
MRad.
8. The method of claim 1 further comprising processing the quenched
biomass feedstock to make a combustible fuel.
9. The method of claim 8 wherein processing comprises converting
the irradiated material utilizing a microorganism.
10. The method of claim 9 wherein converting comprises
saccharifying.
11. The method of claim 9 wherein converting comprises
fermenting.
12. The method of claim 8 wherein the combustible fuel comprises an
alcohol.
13. The method of claim 1, wherein the biomass feedstock is
selected from the group consisting of a low molecular weight sugar,
a starch, paper, paper products, paper waste, wood, particle board,
sawdust, agricultural waste, sewage, silage, grasses, rice hulls,
bagasse, cotton, jute, hemp, flax, bamboo, sisal, abaca, straw,
corn cobs, corn stover, switchgrass, alfalfa, hay, coconut hair,
synthetic celluloses, seaweed, algae, and mixtures thereof.
Description
TECHNICAL FIELD
This invention relates to processing biomass, such as methods and
systems for processing biomass.
BACKGROUND
Various carbohydrates, such as cellulosic and lignocellulosic
materials, e.g., in fibrous form, are produced, processed, and used
in large quantities in a number of applications. Often such
materials are used once, and then discarded as waste, or are simply
considered to be waste materials, e.g., sewage, bagasse, sawdust,
and stover.
SUMMARY
Biomass can be processed to alter its structure at one or more
levels. The processed biomass can then be used, for example as a
source of materials and/or fuel.
In general, the invention pertains to methods of changing a
molecular and/or a supramolecular structure of a biomass feedstock.
As will be discussed below, in some implementations, the methods
include irradiating and quenching the biomass feedstock. In other
implementations, the methods include irradiating the feedstock,
cooling the feedstock, and again irradiating the feedstock.
Carbohydrate-containing materials (e.g., biomass materials or
biomass-derived materials, such as starchy materials, cellulosic
materials, lignocellulosic materials, or biomass materials that are
or that include significant amounts of low molecular weight sugars
(e.g., monosaccharides, disaccharides, or trisaccharides), can be
processed to change their structure, and products can be made from
the structurally changed materials. For example, many of the
methods described herein can provide cellulosic and/or
lignocellulosic materials that have a lower molecular weight and/or
crystallinity relative to a native material. Many of the methods
provide materials that can be more readily utilized by a variety of
microorganisms to produce useful products, such as hydrogen,
alcohols (e.g., ethanol or butanol), organic acids (e.g., acetic
acid), hydrocarbons, co-products (e.g., proteins) or mixtures of
any of these. Many of the products obtained, such as ethanol or
n-butanol, can be utilized as a fuel for powering cars, trucks,
tractors, ships or trains, e.g., as an internal combustion fuel or
as a fuel cell feedstock. Many of the products obtained can also be
utilized to power aircraft, such as planes, e.g., having jet
engines or helicopters. In addition, the products described herein
can be utilized for electrical power generation, e.g., in a
conventional steam generating plant or in a fuel cell plant.
In one aspect, the invention features methods that include
quenching a biomass feedstock that has been irradiated to ionize
the biomass feedstock so that the feedstock has a first level of
radicals which are detectable with an electron spin resonance
spectrometer, to an extent that the radicals are at a second level
lower than the first level. Some methods further include processing
the irradiated and quenched biomass feedstock to produce a
product.
Some implementations include one or more of the following
features.
Quenching can include quenching the radicals to a level that is no
longer detectable with the electron spin resonance spectrometer,
e.g., less than about 10.sup.14 spins. Quenching can include
applying pressure to the biomass, e.g., a pressure of greater than
about 1000 psi. Pressure can be applied together with the
application of heat. Quenching can include contacting the biomass
with a gas capable of reacting with the radicals, e.g., contacting
the biomass with a fluid capable of penetrating into the biomass
and reacting with the radicals. Quenching can also, or
alternatively, include contacting the biomass with an antioxidant.
In some cases, the biomass feedstock includes an antioxidant
dispersed therein, and quenching includes contacting the
antioxidant dispersed in the biomass feedstock with the
radicals.
In another aspect, the invention features a method including
irradiating a biomass feedstock that has been prepared by reducing
one or more dimensions of individual pieces of the biomass
feedstock, using an apparatus comprising an accelerator configured
to accelerate particles, such as electrons or ions, wherein the
apparatus is capable of processing greater than 1,000 tons of
biomass material per year, e.g., greater than 10,000, 25,000,
50,000, 100,000, or even greater than 1,000,000 tons of biomass per
year.
In a further aspect, the invention features irradiating a biomass
feedstock, e.g., with ionizing radiation of electrons or ions, to
change a molecular and/or supramolecular structure of the biomass
feedstock, cooling the biomass feedstock, and then re-irradiating
the biomass feedstock. The two applications of radiation can be the
same or different, e.g., the same kind, such as electrons at the
same level.
The invention also features products formed by these methods, and
systems for performing the methods.
Some implementations of these methods include one or more of the
following features.
The biomass feedstock can be cooled to an extent that after cooling
the biomass is at a temperature below its initial temperature prior
to irradiation. Cooling of the biomass can include contacting the
biomass with a fluid at a temperature below the initial temperature
of the biomass or below the temperature of the biomass after
irradiation.
Each irradiation of the biomass feedstock can be performed as the
biomass feedstock is being pneumatically conveyed in a fluid.
Radiation can be applied as the biomass feedstock falls under the
influence of gravity. For example, the biomass can be conveyed from
a first belt at a first height and captured by a second belt at a
second level, lower than the first level, the trailing edge of the
first belt and the leading edge of the second belt defining a gap,
and ionizing radiation can be applied to the biomass feedstock in
the defined gap. During irradiation the biomass can be conveyed
past a particle gun and through a beam of charged particles. The
biomass feedstock may have a bulk density of less than about 0.25
g/cm.sup.3 in a region under and/or above the beam.
In another aspect, the invention features methods of changing a
molecular structure and/or a supramolecular structure of a starchy
material or of a low molecular weight sugar, such as sucrose, in a
biomass feedstock comprising at least about 10 percent by weight of
the low molecular weight sugar. The methods include processing a
treated biomass feedstock to produce a product, the treated biomass
feedstock having been prepared by pretreating a biomass feedstock
using a pretreatment method that changes the molecular structure
and/or supramolecular structure of the starchy material or of the
low molecular weight sugar portion, selected from radiation,
sonication, pyrolysis, and oxidation.
Any of the above aspects of the invention can, in some
implementations, include one or more of the following features.
The method can further include treating the biomass feedstock with
one or more other pretreatment methods, wherein the other
pretreatment methods are selected from sonication, pyrolysis, and
oxidation.
Radiation can be in the form of an electron beam, which can be
applied, for example, at a total dosage of between about 10 MRad
and about 50 MRad. The radiation can be ionizing radiation.
Processing can include making a combustible fuel. In some cases,
processing includes converting the irradiated material utilizing a
microorganism having the ability to convert at least about 1
percent by weight of the biomass to the fuel.
In some implementations, processing comprises fermenting the
feedstock, aerobically or anaerobically, to produce a product such
as a fuel, e.g., ethanol. For example, processing may comprise
contacting the feedstock with a microorganism having the ability to
convert at least a portion, e.g., at least about 1 percent by
weight, of the feedstock to the product. The microorganism can be a
natural microorganism or an engineered microorganism. For example,
the microorganism can be a bacterium, e.g., a cellulolytic
bacterium, a fungus, e.g., a yeast, a plant or a protist, e.g., an
algae, a protozoa or a fungus-like protist, e.g., a slime mold.
When the organisms are compatible, mixtures may be utilized.
The product can include one or more of hydrogen, organic acids,
proteins, hydrocarbons, and alcohols, e.g., ethanol, n-propanol,
isopropanol, n-butanol, and mixtures thereof. Other examples of
products that may be produced by the methods disclosed herein
include mono- and polyfunctional C1-C6 alkyl alcohols, mono- and
poly-functional carboxylic acids, C1-C6 hydrocarbons, and
combinations thereof. Other examples of alcohols include methanol,
ethylene glycol, propylene glycol, 1,4-butane diol, glycerin, and
combinations thereof. Carboxylic acids include formic acid, acetic
acid, propionic acid, butyric acid, valeric acid, caproic acid,
palmitic acid, stearic acid, oxalic acid, malonic acid, succinic
acid, glutaric acid, oleic acid, linoleic acid, glycolic acid,
lactic acid, .gamma.-hydroxybutyric acid, and combinations thereof.
Hydrocarbons include methane, ethane, propane, pentane, n-hexane,
and combinations thereof. Many of these products may be used as
fuels.
The method can further include preparing the biomass feedstock by
reducing one or more dimensions of individual pieces of the biomass
feedstock.
In some cases, the biomass feedstock has internal fibers, and the
biomass feedstock has been sheared to an extent that its internal
fibers are substantially exposed. The biomass feedstock can in some
cases include or be made up of discrete fibers and/or particles
having a maximum dimension of not more than about 0.5 mm.
The biomass feedstock can be prepared and then pretreated, or
pretreated and then prepared. The pretreatment method can be
selected from, e.g., radiation, such as radiation from a beam of
electrons or ions, sonication, pyrolysis, and oxidation. In some
embodiments, at least one of the pretreatment methods, e.g.,
radiation, is performed on the biomass feedstock while the biomass
feedstock is exposed to air, nitrogen, oxygen, helium, or argon. In
some embodiments, pretreatment can include pretreating the biomass
feedstock with steam explosion.
In some embodiments, reducing one or more dimensions of individual
pieces of biomass includes shearing, wet or dry grinding, cutting,
squeezing, compressing or mixtures of any of these processes. For
example, shearing can be performed with a rotary knife cutter. The
shearing can produce fibers having an average length-to-diameter
ratio of greater than 5/1. In some embodiments, the prepared
biomass can have a BET surface area of greater than 0.25 m.sup.2/g.
The biomass can be sheared to an extent that internal fibers of the
biomass are substantially exposed. The biomass can be sheared to an
extent that it has a bulk density of less than about 0.35
g/cm.sup.3.
In some embodiments, two or more pretreatment methods can be
applied to the biomass feedstock, for example radiation and
sonication, radiation and oxidation, radiation and pyrolization,
sonication and oxidation, sonication and pyrolization, or oxidation
and pyrolization. The two or more processes can be performed in any
order or at or about the same time.
In some embodiments, the change in molecular structure and/or
change in supramolecular structure of the biomass, e.g., the
cellulosic or lignocellulosic material or low molecular weight
sugar or starchy material, can include a change in any one or more
of an average molecular weight, average crystallinity, surface
area, degree of polymerization, porosity, branching, grafting,
domain size or number, a change in kind or number of chemical
functional groups, and a change in formula weight. For example, the
change in molecular structure and/or supramolecular structure can
include a decrease in either one or both of an average molecular
weight and average crystallinity or an increase in either one or
both of surface area and porosity.
In some instances, functionalized biomass (biomass in which the
number and/or kind of functional groups has been changed) is more
soluble and more readily utilized by microorganisms in comparison
to un-functionalized biomass. In addition, many of the
functionalized materials described herein are less prone to
oxidation and can have enhanced long-term stability under ambient
conditions.
In some embodiments, at least one pretreatment method can be
performed on biomass in which less than about 25 percent by weight
of the biomass is in a swollen state, the swollen state being
characterized as having a volume of more than about 2.5 percent
higher than an unswollen state. In other embodiments, the biomass
is mixed with or includes a swelling agent. For example, in any
method described herein, the biomass can be mixed with or and
include a swelling agent, and the biomass can receive a dose of
less than about 10 Mrad of radiation.
The pretreated biomass material can further include, optionally, a
buffer, such as sodium bicarbonate or ammonium chloride, an
electrolyte, such as potassium chloride or sodium chloride, a
growth factor, such as biotin, and/or a base pair such as uracil, a
surfactant, a mineral, or a chelating agent.
In some cases, pretreatment is performed while the biomass
feedstock is exposed to air, nitrogen, oxygen, helium or argon.
Pretreatment may be performed under pressure, e.g., under a
pressure of greater than about 2.5 atmospheres. The methods
described herein may further include oxidizing the biomass prior to
pretreatment.
The biomass feedstock may include, for example, paper, paper
products, paper waste, wood, particle board, sawdust, agricultural
waste, sewage, silage, grasses, rice hulls, bagasse, cotton, jute,
hemp, flax, bamboo, sisal, abaca, straw, corn cobs, corn stover,
switchgrass, alfalfa, hay, rice hulls, coconut hair, cotton,
synthetic celluloses, seaweed, algae, and mixtures thereof. The
biomass may in some cases include a synthetic material.
The biomass can in some cases include a carbohydrate that includes
one or more .beta.-1,4-linkages and has a number average molecular
weight between about 3,000 and 50,000.
In some implementations, the biomass material includes a starch,
e.g., corn starch, wheat starch, potato starch or rice starch, a
derivative of starch, or a material that includes starch, such as
an edible food product or a crop. For example the starchy material
can be arracacha, buckwheat, banana, barley, cassaya, kudzu, oca,
sago, sorghum, regular household potatoes, sweet potato, taro,
yams, or one or more beans, such as fava beans, lentils, or
peas.
In other implementations, the biomass material is or includes a low
molecular weight sugar. For example, the biomass materials can
include at least about 0.5 percent by weight of a low molecular
weight sugar, e.g., at least about 2, 3, 4, 5, 6, 7, 8, 9, 10,
12.5, 25, 35, 50, 60, 70, 80, 90 or even at least about 95 percent
by weight of the low molecular weight sugar. In some instances, the
biomass is composed substantially of the low molecular weight
sugar, e.g., greater than 95 percent by weight, such as 96, 97, 98,
99 or substantially 100 percent by weight of the low molecular
weight sugar. Biomass materials that include low molecular weight
sugars can be agricultural products or food products, such as
sugarcane and sugar beets, or an extract therefrom, e.g., juice
from sugarcane or sugar beets. Specific examples of low molecular
weight sugars include cellobiose, lactose, sucrose, glucose and
xylose, along with derivatives thereof. Processing low molecular
weight sugars by any of the methods described herein can make the
resulting products more soluble and/or easier to utilize by
microbes.
In any of the methods disclosed herein, radiation may be applied
from a device that is in a vault.
The term "fibrous material," as used herein, is a material that
includes numerous loose, discrete and separable fibers. For
example, a fibrous material can be prepared from a bleached Kraft
paper fiber source by shearing, e.g., with a rotary knife
cutter.
The term "screen," as used herein, means a member capable of
sieving material according to size. Examples of screens include a
perforated plate, cylinder or the like, or a wire mesh or cloth
fabric.
The term "pyrolysis," as used herein, means to break bonds in a
material by the application of heat energy. Pyrolysis can occur
while the subject material is under vacuum, or immersed in a
gaseous material, such as an oxidizing gas, e.g., air or oxygen, or
a reducing gas, such as hydrogen.
Oxygen content is measured by elemental analysis by pyrolyzing a
sample in a furnace operating at 1300.degree. C. or above.
The terms "biomass" refers to any non-fossilized, i.e., renewable,
organic matter. The various types of biomass include plant biomass
(defined below), microbial biomass, animal biomass (any animal
by-product, animal waste, etc.) and municipal waste biomass
(residential and light commercial refuse with recyclables such as
metal and glass removed).
The term "plant biomass" and "lignocellulosic biomass" refer to
virtually any plant-derived organic matter (woody or non-woody).
Plant biomass can include, but is not limited to, agricultural or
food crops (e.g., sugarcane, sugar beets or corn kernels) or an
extract therefrom (e.g., sugar from sugarcane and corn starch from
corn), agricultural crop wastes and residues such as corn stover,
wheat straw, rice straw, sugar cane bagasse, and the like. Plant
biomass further includes, but is not limited to, trees, woody
energy crops, wood wastes and residues such as softwood forest
thinnings, barky wastes, sawdust, paper and pulp industry waste
streams, wood fiber, and the like. Additionally, grass crops, such
as switchgrass and the like have potential to be produced on a
large-scale as another plant biomass source. For urban areas, the
best potential plant biomass feedstock includes yard waste (e.g.,
grass clippings, leaves, tree clippings, and brush) and vegetable
processing waste.
"Lignocellulosic feedstock," is any type of plant biomass such as,
but not limited to, non-woody plant biomass, cultivated crops, such
as, but not limited to, grasses, for example, but not limited to,
C4 grasses, such as switchgrass, cord grass, rye grass, miscanthus,
reed canary grass, or a combination thereof, or sugar processing
residues such as bagasse, or beet pulp, agricultural residues, for
example, soybean stover, corn stover, rice straw, rice hulls,
barley straw, corn cobs, wheat straw, canola straw, rice straw, oat
straw, oat hulls, corn fiber, recycled wood pulp fiber, sawdust,
hardwood, for example aspen wood and sawdust, softwood, or a
combination thereof. Further, the lignocellulosic feedstock may
include cellulosic waste material such as, but not limited to,
newsprint, cardboard, sawdust, and the like.
Lignocellulosic feedstock may include one species of fiber or
alternatively, lignocellulosic feedstock may include a mixture of
fibers that originate from different lignocellulosic feedstocks.
Furthermore, the lignocellulosic feedstock may comprise fresh
lignocellulosic feedstock, partially dried lignocellulosic
feedstock, fully dried lignocellulosic feedstock or a combination
thereof.
For the purposes of this disclosure, carbohydrates are materials
that are composed entirely of one or more saccharide units or that
include one or more saccharide units. The saccharide units can be
functionalized about the ring with one or more functional groups,
such as carboxylic acid groups, amino groups, nitro groups, nitroso
groups or nitrile groups and still be considered carbohydrates.
Carbohydrates can be polymeric (e.g., equal to or greater than
10-mer, 100-mer, 1,000-mer, 10,000-mer, or 100,000-mer), oligomeric
(e.g., equal to or greater than a 4-mer, 5-mer, 6-mer, 7-mer,
8-mer, 9-mer or 10-mer), trimeric, dimeric, or monomeric. When the
carbohydrates are formed of more than a single repeat unit, each
repeat unit can be the same or different.
Examples of polymeric carbohydrates include cellulose, xylan,
pectin, and starch, while cellobiose and lactose are examples of
dimeric carbohydrates. Examples of monomeric carbohydrates include
glucose and xylose.
Carbohydrates can be part of a supramolecular structure, e.g.,
covalently bonded into the structure. Examples of such materials
include lignocellulosic materials, such as those found in wood.
A starchy material is one that is or includes significant amounts
of starch or a starch derivative, such as greater than about 5
percent by weight starch or starch derivative. For purposes of this
disclosure, a starch is a material that is or includes an amylose,
an amylopectin, or a physical and/or chemical mixture thereof,
e.g., a 20:80 or 30:70 percent by weight mixture of amylose to
amylopectin. For example, rice, corn, and mixtures thereof are
starchy materials. Starch derivatives include, e.g., maltodextrin,
acid-modified starch, base-modified starch, bleached starch,
oxidized starch, acetylated starch, acetylated and oxidized starch,
phosphate-modified starch, genetically-modified starch and starch
that is resistant to digestion.
For purposes of this disclosure, a low molecular weight sugar is a
carbohydrate or a derivative thereof that has a formula weight
(excluding moisture) that is less than about 2,000, e.g., less than
about 1,800, 1,600, less than about 1,000, less than about 500,
less than about 350 or less than about 250. For example, the low
molecular weight sugar can be a monosaccharide, e.g., glucose or
xylose, a disaccharide, e.g., cellobiose or sucrose, or a
trisaccharide.
A combustible fuel is a material capable of burning in the presence
of oxygen. Examples of combustible fuels include ethanol,
n-propanol, n-butanol, hydrogen and mixtures of any two or more of
these.
Swelling agents as used herein are materials that cause a
discernable swelling, e.g., a 2.5 percent increase in volume over
an unswollen state of cellulosic and/or lignocellulosic materials,
when applied to such materials as a solution, e.g., a water
solution. Examples include alkaline substances, such as sodium
hydroxide, potassium hydroxide, lithium hydroxide and ammonium
hydroxides, acidifying agents, such as mineral acids (e.g.,
sulfuric acid, hydrochloric acid and phosphoric acid), salts, such
as zinc chloride, calcium carbonate, sodium carbonate,
benzyltrimethylammonium sulfate, and basic organic amines, such as
ethylene diamine.
A "sheared material," as used herein, is a material that includes
discrete fibers in which at least about 50% of the discrete fibers
have a length/diameter (L/D) ratio of at least about 5, and that
has an uncompressed bulk density of less than about 0.6 g/cm.sup.3.
A sheared material is thus different from a material that has been
cut, chopped or ground.
Changing a molecular structure of a biomass feedstock, as used
herein, means to change the chemical bonding arrangement, such as
the type and quantity of functional groups, or conformation of the
structure. For example, the change in the molecular structure can
include changing the supramolecular structure of the material,
oxidation of the material, changing an average molecular weight,
changing an average crystallinity, changing a surface area,
changing a degree of polymerization, changing a porosity, changing
a degree of branching, grafting on other materials, changing a
crystalline domain size, or an changing an overall domain size.
This application incorporates by reference herein the entire
contents of International Application No. PCT/US2007/022719, filed
on Oct. 26, 2007. The full disclosures of each of the following
U.S. patent applications, which are being filed concurrently
herewith, are hereby incorporated by reference herein: Ser. Nos.
12/417,707, 12/417,720, 12/417,699, 12/417,840, 12/417,731,
12/417,900, 12/417,723, 12/417,786, and 12/417,904.
Unless otherwise defined, all technical and scientific terms used
herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, suitable methods and materials are described below. All
publications, Appendices, patent applications, patents, and other
references mentioned herein or attached hereto are incorporated by
reference in their entirety for all that they contain. In case of
conflict, the present specification, including definitions, will
control. In addition, the materials, methods, and examples are
illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent
from the following detailed description, and from the claims.
DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram illustrating conversion of biomass into
products and co-products.
FIG. 2 is block diagram illustrating conversion of a fiber source
into a first and second fibrous material.
FIG. 3 is a cross-sectional view of a rotary knife cutter.
FIG. 4 is block diagram illustrating conversion of a fiber source
into a first, second and third fibrous material.
FIG. 5 is block diagram illustrating densification of a
material.
FIG. 6 is a perspective view of a pellet mill.
FIG. 7A is a densified fibrous material in pellet form.
FIG. 7B is a transverse cross-section of a hollow pellet in which a
center of the hollow is in-line with a center of the pellet.
FIG. 7C is a transverse cross-section of a hollow pellet in which a
center of the hollow is out of line with the center of the
pellet.
FIG. 7D is a transverse cross-section of a tri-lobal pellet.
FIG. 8 is a block diagram illustrating a treatment sequence for
processing feedstock.
FIG. 9 is a perspective, cut-away view of a gamma irradiator housed
in a concrete vault.
FIG. 10 is an enlarged perspective view of region R of FIG. 9.
FIG. 11 is a block diagram illustrating an electron beam
irradiation feedstock pretreatment sequence.
FIG. 11A is a schematic representation of biomass being ionized,
and then oxidized or quenched.
FIG. 11B is a schematic side view of a system for irradiating a low
bulk density material, while FIG. 11C is cross-sectional of the
system taken along 11C-11C.
FIG. 11D is a schematic cross-sectional view of a fluidized bed
system for irradiating a low bulk density material.
FIG. 11E is a schematic side-view of another system for irradiating
a low bulk density material.
FIG. 12 is a schematic view of a system for sonicating a process
stream of cellulosic material in a liquid medium.
FIG. 13 is a schematic view of a sonicator having two transducers
coupled to a single horn.
FIG. 14 is a block diagram illustrating a pyrolytic feedstock
pretreatment system.
FIG. 15 is a cross-sectional side view of a pyrolysis chamber.
FIG. 16 is a cross-sectional side view of a pyrolysis chamber.
FIG. 17 is a cross-sectional side view of a pyrolyzer that includes
a heated filament.
FIG. 18 is a schematic cross-sectional side view of a Curie-Point
pyrolyzer.
FIG. 19 is a schematic cross-sectional side view of a furnace
pyrolyzer.
FIG. 20 is a schematic cross-sectional top view of a laser
pyrolysis apparatus.
FIG. 21 is a schematic cross-sectional top view of a tungsten
filament flash pyrolyzer.
FIG. 22 is a block diagram illustrating an oxidative feedstock
pretreatment system.
FIG. 23 is block diagram illustrating a general overview of the
process of converting a fiber source into a product, e.g.,
ethanol.
FIG. 24 is a cross-sectional view of a steam explosion
apparatus.
FIG. 25 is a schematic cross-sectional side view of a hybrid
electron beam/sonication device.
FIG. 26 is a block diagram illustrating a dry milling process for
corn kernels.
FIG. 27 is a block diagram illustrating a wet milling process for
corn kernels.
FIG. 28 is a scanning electron micrograph of a fibrous material
produced from polycoated paper at 25.times. magnification. The
fibrous material was produced on a rotary knife cutter utilizing a
screen with 1/8 inch openings.
FIG. 29 is a scanning electron micrograph of a fibrous material
produced from bleached Kraft board paper at 25.times.
magnification. The fibrous material was produced on a rotary knife
cutter utilizing a screen with 1/8 inch openings.
FIG. 30 is a scanning electron micrograph of a fibrous material
produced from bleached Kraft board paper at 25.times.
magnification. The fibrous material was twice sheared on a rotary
knife cutter utilizing a screen with 1/16 inch openings during each
shearing.
FIG. 31 is a scanning electron micrograph of a fibrous material
produced from bleached Kraft board paper at 25.times.
magnification. The fibrous material was thrice sheared on a rotary
knife cutter. During the first shearing, a 1/8 inch screen was
used; during the second shearing, a 1/16 inch screen was used, and
during the third shearing a 1/32 inch screen was used.
FIG. 32 is a schematic side view of a sonication apparatus, while
FIG. 33 is a cross-sectional view through the processing cell of
FIG. 32.
FIG. 34 is a scanning electron micrograph at 1000.times.
magnification of a fibrous material produced from shearing
switchgrass on a rotary knife cutter, and then passing the sheared
material through a 1/32 inch screen.
FIGS. 35 and 36 are scanning electron micrographs of the fibrous
material of FIG. 34 after irradiation with 10 Mrad and 100 Mrad
gamma rays, respectively, at 1000.times. magnification.
FIG. 37 is a scanning electron micrographs of the fibrous material
of FIG. 34 after irradiation with 10 Mrad and sonication at
1000.times. magnification.
FIG. 38 is a scanning electron micrographs of the fibrous material
of FIG. 34 after irradiation with 100 Mrad and sonication at
1000.times. magnification.
FIG. 39 is an infrared spectrum of Kraft board paper sheared on a
rotary knife cutter.
FIG. 40 is an infrared spectrum of the Kraft paper of FIG. 39 after
irradiation with 100 Mrad of gamma radiation.
FIG. 41 is a schematic view of a process for biomass
conversion.
FIG. 42 is schematic view of another process for biomass
conversion.
DETAILED DESCRIPTION
Systems and processes are described herein that can use various
biomass materials, such as cellulosic materials, lignocellulosic
materials, starchy materials or materials that are or that include
low molecular weight sugars, as feedstock materials. Such materials
are often readily available, but can be difficult to process, e.g.,
by fermentation, or can gives sub-optimal yields at a slow rate. In
some cases, the difficulty in processing stems at least in part
from the recalcitrance of the feedstock. Processing steps are
described herein that can reduce this recalcitrance and thereby
facilitate conversion of the biomass feedstock to a desired
product.
In the processes described herein, feedstock materials are first
physically prepared for processing, often by size reduction of raw
feedstock materials. Physically prepared feedstock can then be
pretreated or processed using one or more of radiation (which may
in some cases be under controlled thermal conditions), sonication,
oxidation, pyrolysis, and steam explosion. The various pretreatment
systems and methods can be used in combinations of two, three, or
even four of these technologies. Other techniques which may be used
to enhance the processing of the feedstock are described herein,
for example cooling the feedstock between irradiating steps and
quenching the biomass feedstock after irradiation.
Functionalized materials are also disclosed herein, having desired
types and amounts of functionality, such as carboxylic acid groups,
enol groups, aldehyde groups, ketone groups, nitrile groups, nitro
groups, or nitroso groups, which can be prepared using the methods
described herein. Such functionalized materials can be, e.g., more
soluble, easier to utilize by various microorganisms or can be more
stable over the long term, e.g., less prone to oxidation.
In some cases, the feedstock can include low molecular weight
sugars or starchy materials, as will be discussed in detail
herein.
Types of Biomass
Generally, any biomass material that is or includes carbohydrates
composed entirely of one or more saccharide units or that include
one or more saccharide units can be processed by any of the methods
described herein. For example, the biomass material can be
cellulosic or lignocellulosic materials, starchy materials, such as
kernels of corn, grains of rice or other foods, or materials that
are or that include one or more low molecular weight sugars, such
as sucrose or cellobiose.
For example, such materials can include paper, paper products,
wood, wood-related materials, particle board, grasses, rice hulls,
bagasse, cotton, jute, hemp, flax, bamboo, sisal, abaca, straw,
corn cobs, rice hulls, coconut hair, algae, seaweed, cotton,
synthetic celluloses, or mixtures of any of these. Suitable
materials include those listed in the Summary section, above.
Fiber sources include cellulosic fiber sources, including paper and
paper products (e.g., polycoated paper and Kraft paper), and
lignocellulosic fiber sources, including wood, and wood-related
materials, e.g., particle board. Other suitable fiber sources
include natural fiber sources, e.g., grasses, rice hulls, bagasse,
cotton, jute, hemp, flax, bamboo, sisal, abaca, straw, corn cobs,
rice hulls, coconut hair; fiber sources high in .alpha.-cellulose
content, e.g., cotton; and synthetic fiber sources, e.g., extruded
yarn (oriented yarn or un-oriented yarn). Natural or synthetic
fiber sources can be obtained from virgin scrap textile materials,
e.g., remnants or they can be post consumer waste, e.g., rags. When
paper products are used as fiber sources, they can be virgin
materials, e.g., scrap virgin materials, or they can be
post-consumer waste. Aside from virgin raw materials,
post-consumer, industrial (e.g., offal), and processing waste
(e.g., effluent from paper processing) can also be used as fiber
sources. Also, the fiber source can be obtained or derived from
human (e.g., sewage), animal or plant wastes. Additional fiber
sources have been described in U.S. Pat. Nos. 6,448,307, 6,258,876,
6,207,729, 5,973,035 and 5,952,105.
Microbial biomass includes biomass derived from naturally occurring
or genetically modified unicellular organisms and/or multicellular
organisms, e.g., organisms from the ocean, lakes, bodies of water,
e.g., salt water or fresh water, or on land, and that contains a
source of carbohydrate (e.g., cellulose). Microbial biomass can
include, but is not limited to, for example protists (e.g., animal
(e.g., protozoa such as flagellates, amoeboids, ciliates, and
sporozoa) and plant (e.g., algae such alveolates,
chlorarachniophytes, cryptomonads, euglenids, glaucophytes,
haptophytes, red algae, stramenopiles, and viridaeplantae)),
seaweed, plankton (e.g., macroplankton, mesoplankton,
microplankton, nanoplankton, picoplankton, and femptoplankton),
phytoplankton, bacteria (e.g., gram positive bacteria, gram
negative bacteria, and extremophiles), yeast and/or mixtures of
these. In some instances, microbial biomass can be obtained from
natural sources, e.g., the ocean, lakes, bodies of water, e.g.,
salt water or fresh water, or on land. Alternatively or in
addition, microbial biomass can be obtained from culture systems,
e.g., large scale dry and wet culture systems.
Animal biomass includes any organic waste material such as
animal-derived waste material or excrement or human waste material
or excrement (e.g., manure and sewage).
In some embodiments, the carbohydrate is or includes a material
having one or more .beta.-1,4-linkages and having a number average
molecular weight between about 3,000 and 50,000. Such a
carbohydrate is or includes cellulose (I), which is derived from
(.beta.-glucose 1) through condensation of
.beta.(1.fwdarw.4)-glycosidic bonds. This linkage contrasts itself
with that for .alpha.(1.fwdarw.4)-glycosidic bonds present in
starch and other carbohydrates.
##STR00001## Starchy Materials
Starchy materials include starch itself, e.g., corn starch, wheat
starch, potato starch or rice starch, a derivative of starch, or a
material that includes starch, such as an edible food product or a
crop. For example, the starchy material can be arracacha,
buckwheat, banana, barley, cassaya, kudzu, oca, sago, sorghum,
regular household potatoes, sweet potato, taro, yams, or one or
more beans, such as favas, lentils or peas. A blend of any two or
more starchy materials is also a starchy material. Starch sources
include, e.g., wheat, barley, corn and potatoes. In particular
embodiments, the starchy material is derived from corn. Various
corn starches and derivatives are described in "Corn Starch," Corn
Refiners Association (11.sup.th Edition, 2006), which is attached
hereto as Appendix A.
A starch (e.g., CAS#9005-25-8 and chemical formula
(C.sub.6H.sub.10O.sub.5).sub.n) generally comprises a mixture of
amylose and amylopectin (usually in 20:80 or 30:70 ratios) and
generally exists as a homopolymer of repeating anhydroglucose units
joined by an -glucosidic on the next starch unit through hemiacetal
linkages. Starch molecules typically are made up of 1,4-linkages
are referred to as amylose while 1,6-linkages serve as the
branching point in branched starch molecules called
amylopectin.
Granular Structure
TABLE-US-00001 TABLE 1 Granule Size of Various Starches Granule
Size Range (.mu.m) Average size Starch Species (Coulter Counter)
(.mu.m) Waxy Rice 2-13 5.5 High Amylose Corn 4-22 9.8 Corn 5-25
14.3 Cassava 3-28 14 Sorghum 3-27 16 Wheat 3-34 6.5, 19.5 Sweet
Potato 4-40 18.5 Arrowroot 9-40 23 Sago 15-50 33 Potato 10-70 36
Canna (Aust. Arrowroot) 22-85 53
Plants store starch within specialized organelles called
amyloplasts where they are deposited to form granules. These
granules are comprised of newly-synthesized starch layered around a
hilum nucleus, and vary in diameter from 2 to 130 microns. The size
and shape of the granule is characteristic of the plant's origin
and serves as a way of identifying the source of a particular
starch (Table 1). The structure of the granule of grain is
crystalline with the starch molecules orienting in such a way as to
form radially oriented crystals giving rise to the phenomenon of
birefringence. When a beam of polarized light is directed through a
starch granule, the granule is divided by dark lines into four
wedge-shaped sections. This cross-hatching or cross is
characteristic of spherocrystalline structures.
Amylose
##STR00002##
Amylose molecules consist of single mostly-unbranched chains with
500-20,000 .alpha.-(1,4)-D-glucose units depending on the source.
The .alpha.(1,4) bonds promote the formation of a helix structure.
The structural formula of amylose is pictured in FIG. 2 where the
number of repeated glucose subunits (n) can be many thousands
(usually in the range of 300 to 3000). Amylose starch is less
readily digested than amylopectin; however, it takes up less space
so is preferred for storage in plants. Amylose makes up about 30%
of the stored starch in plants. The digestive enzyme amylase works
on the ends of the starch molecule, breaking it down into
sugars.
Amylose molecules contribute to gel formation because the linear
chains can orient parallel to each other, moving close enough
together to bond. Probably due to the ease with which amylose
molecules slip past each other in the cooked paste, they do not
contribute significantly to viscosity.
Amylopectin
##STR00003##
Amylopectin is formed by non-random .alpha.-(1,6)-branching of the
amylose-type .alpha.-(1,4)-D-glucose structure. As can be seen in
FIG. 3, glucose units are linked in a linear way with .alpha.(1,4)
bonds. Branching takes place with .alpha.(1,6) bonds occurring
every 24 to 30 glucose units and is determined by branching
enzymes. Each amylopectin molecule contains a million or so
residues, about 5% of which form the branch points.
The branched amylopectin molecules give viscosity to the cooked
paste due to the role it serves in maintaining the swollen granule.
Their side chains and bulky shape keep amylopectin molecules from
orienting closely enough to hydrogen bond together, so they do not
usually contribute to gel formation.
Source
Plants hydrolyze starch releasing the glucose subunits when energy
is required. By far the largest source of starch is corn (maize)
with other commonly used sources being wheat, potato, tapioca and
rice. The relative proportions of amylose to amylopectin and
1,6-linkage branch-points are established genetically and are
relatively constant for each species of starch. For example,
amylomaizes contain over 50% amylase, whereas "waxy" maize has
almost none (.about.3%).
Unprocessed Starch
Starch that is produced by the corn wet milling process and then
dried is referred to as common, regular, or unmodified corn starch.
Various forms of corn starch exist including, fine or coarse
powders, flakes, pearls or even larger particles. Unmodified starch
can be minimally processed by adjusting the pH, by mild heat
treatment, or by adding small quantities of chemicals or adjuvants
before or after drying in order to optimize performance. As an
example, enzyme conversion of starch to sugars can be accelerated
by adjusting the pH of the starch.
By far the most consumed polysaccharide in the human diet is
starch. Starch (in particular cornstarch) is used in cooking for
thickening foods such as sauces. In industry, it is used in the
manufacturing of adhesives, paper, textiles, and as a mold in the
manufacture of sweets such as wine gums and jelly beans.
Papermaking is the largest non-food application for starches
globally, consuming millions of metric tons annually. In a typical
sheet of copy paper for example, the starch content may be as high
as 8%. Both chemically modified and unmodified starches are used in
papermaking.
The chemical composition of starch, highly oxygenated carbon
molecules, makes starch an excellent product for use as a chemical
feedstock.
Genetically Modified Starch
Genetically modified starch, which refers to starch from
genetically engineered plants, has been modified to reduce the need
for chemical processing (reducing cost, toxicity, or
environmentally hazardous processes), or in order to produce novel
carbohydrates which might not naturally occur in the plant species
being harvested. The modification in this sense refers to the
genetic engineering of the plant DNA, and not the later processing
or treatment of the starch or starch granules.
Genetically modified starch is of particular interest in the
manufacture of biodegradable polymers and non-cellulose feedstock
in the paper industry, as well as the creation of new food
additives. For example, waxy maize was studied extensively in the
1950's for it's desirable properties. Waxy maize starch, which is
essentially 100% amylopectin, yields pastes that are almost clear
when cool, non-congealing, and when dried in thin films, yields a
translucent, water-soluble coating often used for thickening a wide
variety of prepared foods. Genetic modification of this starch to
try and increase the amylose content could potentially result in an
excellent film former and might be spun into a fiber. Research in
this area resulted in the commercial development of two corn
hybrids, one containing about 55%, the other about 70% amylose, and
recently research has resulted in developing a starch with 80%
amylose.
Modified Starch
Modified starch is a food additive which is prepared by treating
starch or starch granules, causing the starch to be partially
degraded. Modified starch is used as a thickening agent,
stabilizer, or an emulsifier. Apart from food products, modified
starch is also found in pharmaceuticals. Starches are modified for
a number of reasons including, to increase their stability to
excessive heat, acid, and freezing; to change their texture; or to
lengthen or shorten gelatinization time.
Acid-Modified Starch
Acid-treated starch, usually simply referred to as "modified
starch", is prepared by treating starch or starch granules with
inorganic acids. The primary reaction taking place during acid
treatment is hydrolysis of glucosidic bonds in starch molecules.
Acid modification reduces the chain length of the starch, but does
not substantially change the molecular configuration. In this
method, a starch-water suspension is agitated while being subjected
to mild treatment with dilute mineral acid at temperatures elevated
but below the starch gelatinization temperature. Upon achieving the
desired viscosity, the acid is neutralized with sodium carbonate
and the starch is filtered, washed, and dried.
Oxidized Corn Starch
Another method for reducing viscosity is oxidation. Although
oxidizing agents such as chlorine, hydrogen peroxide and potassium
permanganate can be used, oxidized starches produced by the wet
milling process are almost always made using sodium hypochlorite as
the oxidizing agent. Aqueous starch suspensions under agitation are
treated with dilute sodium hypochlorite containing a small excess
of sodium hydroxide (NaOH) and heated to 120.degree. F. When the
desired viscosity is achieved, the oxidized starch slurry is
treated with a reducing agent such as sodium bisulfite to remove
excess hypochlorite, the pH is adjusted, and the starch is
filtered, washed and finally dried. Treatment of starch with an
oxidizing agent randomly converts hydroxyl groups to carboxyl or
carbonyl groups, which results in the cleavage of the adjacent
glucosidic bond. Oxidized starches are used in batters and breading
as they adhere quite well to meats.
Dextrins
Dextrins are a group of low molecular weight carbohydrates produced
by the dry heating or roasting of unmodified starch, with or
without an acid or alkaline catalyst. Other dextrinization methods
utilize a fluid bed, in which unmodified starch is placed in a
reactor and suspended or "fluidized" in a stream of heated air. The
starch is then acidified and heated until the desired end product
is obtained. During dextrinization, the granule is not destroyed
but granule integrity is disrupted. When dextrins are suspended in
water and heated, the granules swell and separate into layers that
eventually break free and disperse. Dextrins are mixtures of linear
.alpha.-(1,4)-linked D-glucose polymers starting with an
.alpha.-(1,6) bond. Industrial production is, in general, performed
by acidic hydrolysis of potato starch. Dextrins are water-soluble,
white to slightly yellow solids that are optically active. Under
analysis, dextrins can be detected with iodine solution, giving a
red coloration.
There are three major types of dextrins: white, yellow, and British
gums. White dextrins have a white color and have reduced
viscosities, and cold water solubilities ranging from 5 to over
90%. White dextrins are used to make very soft gels. Yellow
dextrins (produced with less acid, higher temperatures, and more
time) are yellow in color and have higher water solubility. Yellow
dextrins are used for making high solids pastes that are very tacky
and, when applied in thin films, dry rapidly. Finally, British gums
are produced by adding little or no acid to very dry starch and
then roasting while gradually increasing the temperature. They are
tan to light brown in color and are used to prepare nearly solid
gels through very soft gels to viscous liquids.
Cyclodextrins
Cyclodextrins are non-reducing cyclic glucose oligosaccharides
resulting from the cyclomaltodextrin glucanotransferase catalyzed
degradation of starch. There are three common cyclodextrins with 6,
7 or 8 D-glucopyranonsyl residues (.alpha.-, .beta.-, and
.gamma.-cyclodextrin, respectively) linked by .alpha.-1,4
glycosidic bonds (FIG. 4). All three cyclodextrins have similar
structures (bond lengths and orientations) apart from the
structural necessities of accommodating a different number of
glucose residues. They present a bottomless bowl-shaped (truncated
cone) molecule stiffened by hydrogen bonding between the 3-OH and
2-OH groups around the outer rim. Cyclodextrins are used for
encapsulation for controlled flavor release, masking odors and
tastes, stabilizing emulsions, increasing foaming power, and
controlling or masking color.
Starch Derivatives (Crosslinked and Stabilization)
Starch can be chemically derivatized at the primary and secondary
hydroxyl positions, which imparts different properties than those
found in the parent starch. This is presumably due to disruption of
hydrogen bonds. Two types of derivatives are prepared commercially,
crosslinked/inhibited and stabilization. Crosslinked starches,
sometimes referred to as inhibited starches, are made by reacting
hydroxyl groups on two different molecules within a granule with a
bifunctional agent. Reagents such as phosphorus oxychloride or
sodium trimetaphosphate may be used as crosslinking agents. Very
small amounts of these agents can exert a marked effect on the
behavior of the cooked starch.
Starch can be stabilized against gelling using monofunctional
reagents. These reagents react with hydroxyl groups on the starch
to introduce substituent groups that interfere with hydrogen
bonding effects thereby increasing their water combining capacity
or viscosity, or imparting a positive charge to the starch
molecule. Reagents used in the stabilization of starch through
disruption of hydrogen bonding include, ethylene oxide to produce
hydroxyethyl starch, acetic anhydride to produce starch acetates,
succinic anhydride to produce starch succinates, monosodium
orthophosphate or sodium tripolyphosphate to produce starch
phosphates, and propylene oxide to produce hydroxypropyl starches.
Reagents that impart a positive charge to the starch molecule
include tertiary or quaternary amines to produce cationic
starches.
Pregelatinized Starch
Suspensions of many starches and starch derivatives can be
gelatinized and dried to yield a broad variety of pregelatinized
starches. This is done on a single drum dryer with applicator
rolls. The starch slurry is heated to gelatinize it,
instantaneously dried and ground to desired granulation
requirement. Pregelatinized starch is used to thicken instant
desserts such as puddings, allowing the food to thicken with the
addition of cold water or milk. Similarly, cheese sauce granules
(such as in Macaroni and Cheese or lasagna) or gravy granules may
be thickened with boiling water without the product going lumpy.
Commercial pizza toppings containing modified starch will thicken
when heated in the oven, keeping them on top of the pizza, and then
become runny when cooled.
Bleached Starches
Bleaching by very light oxidation is carried out using sodium
hypochlorite, sodium chlorite, hydrogen peroxide, potassium
permanganate, peracetic acid, or ammonium persulfate with sulfur
dioxide. Interaction with the starch molecules must be very small
since no change occurs in the physical properties of the starch or
its solution except in its color. Theoretically, there will be
production of a few aldehyde or carboxyl groups. Only trace amounts
of sodium chloride, sodium sulfate or sodium acetate remain in the
final product. The bleached starch is recovered on continuous
filters or centrifuges using copious amounts of water to remove
trace amounts of inorganic salts formed from the bleaching agent,
dried and packaged.
Low Molecular Weight Sugars
Biomass materials that include low molecular weight sugars can,
e.g., include at least about 0.5 percent by weight of the low
molecular sugar, e.g., at least about 2, 3, 4, 5, 6, 7, 8, 9, 10,
12.5, 25, 35, 50, 60, 70, 80, 90 or even at least about 95 percent
by weight of the low molecular weight sugar. In some instances, the
biomass is composed substantially of the low molecular weight
sugar, e.g., greater than 95 percent by weight, such as 96, 97, 98,
99 or substantially 100 percent by weight of the low molecular
weight sugar.
Biomass materials that include low molecular weight sugars can be
agricultural products or food products, such as sugarcane and sugar
beets or an extract therefrom, e.g., juice from sugarcane, or juice
from sugar beets. Biomass materials that include low molecular
weight sugars can be substantially pure extracts, such as raw or
crystallized table sugar (sucrose). Low molecular weight sugars
include sugar derivatives. For example, the low molecular weight
sugars can be oligomeric (e.g., equal to or greater than a 4-mer,
5-mer, 6-mer, 7-mer, 8-mer, 9-mer or 10-mer), trimeric, dimeric, or
monomeric. When the carbohydrates are formed of more than a single
repeat unit, each repeat unit can be the same or different.
Specific examples of low molecular weight sugars include
cellobiose, lactose, sucrose, glucose and xylose, along with
derivatives thereof. In some instances, sugar derivatives are more
rapidly dissolved in solution or utilized by microbes to provide a
useful material, such as ethanol or butanol. Several such sugars
and sugar derivatives are shown below.
##STR00004## Ethanol from Low Molecular Weight Sugars
More than half of world ethanol production is produced from sugar
and sugar byproducts, with Brazil being by far the world leader.
Currently, there is no commercial production of ethanol from
sugarcane or sugar beets in the United States, where 97 percent of
ethanol is produced from corn.
Technologically, the process of producing ethanol from sugar is
simpler than converting corn into ethanol. Converting corn into
ethanol requires additional cooking (wet milling process) and the
application of enzymes, whereas the conversion of sugar requires
only a yeast fermentation process. The energy requirement for
converting sugar into ethanol is about half that for corn. However,
the technology and direct energy costs are but one of several
factors that determine the feasibility of ethanol production. Other
factors include relative production costs (including feedstocks),
conversion rates, proximity to processing facilities, alternative
prices and government policies, facility construction and
processing costs. As other countries have shown that it can be
economically feasible to produce ethanol from sugar and other new
feedstocks are researched, interest in the United States in ethanol
production from sugar has increased.
In response to the growing interest around sugar and ethanol, USDA
released a study in July 2006 titled: "The Economic Feasibility of
Ethanol Production from Sugar in the United States" which is
incorporated herein by reference in its entirety. The report found
that at the current market prices for ethanol, converting
sugarcane, sugar beets and molasses to ethanol would be profitable
(see Table 1).
TABLE-US-00002 TABLE 1 Current Market Prices for Ethanol Feedstock
Total Costs* Processing Costs* Corn (wet milling/dry milling):
$1.03/1.05 $0.63/0.52 Raw Sugarcane $2.40 $0.92 Raw Sugar beets
$2.35 $0.77 Molasses** $1.27 $0.36 Raw Sugar** $3.48 $0.36 Refined
sugar** $3.97 $0.36 *Per gallon **Excludes transportation costs
Sugar Beets
Sugar beets are an annual crop grown in 11 states across a variety
of climatic conditions, from the hot climate of the Imperial Valley
of California to the colder climates of Montana and North Dakota.
Sugar beet byproducts include beet pulp, which can be sold for
animal feed, and molasses, which is also sold for animal feed or
further processed to extract more sugar.
Sugar beet processing facilities convert raw sugar beets directly
into refined sugar in a 1-step process. While planted sugar beet
acreage has fallen slightly since the 1990s, sugar production
actually increased due to investments in new processing equipment,
the adoption of new technologies, improved crop varieties and
enhanced technologies for the de-sugaring of molasses. Sugar beets
are very bulky and relatively expensive to transport and must be
processed fairly quickly before the sucrose deteriorates.
Therefore, all sugar beet processing plants are located in the
production areas.
Sugarcane
Sugarcane is a perennial tropical crop produced in four states:
Florida, Hawaii, Louisiana and Texas. Byproducts of sugarcane
processing include molasses and bagasse, the fibrous material that
remains after sugar is pressed from the sugarcane. Bagasse is often
burned as fuel to help power the sugarcane mills. Sugarcane is
initially processed into raw sugar at mills near the cane fields.
Like beets, cane is bulky and relatively expensive to transport and
must be processed as soon as possible to minimize sucrose
deterioration. The raw sugar is then shipped to refineries to
produce refined sugar.
Sugar beets have gained a greater share of U.S. sugar production
over the past decade, now accounting for 58.8 percent of the
nation's sugar output while sugarcane fell to 41.2 percent.
Molasses
The most widely used sugar for ethanol fermentation is blackstrap
molasses which contains about 35-40 wt % sucrose, 15-20 wt % invert
sugars such as glucose and fructose, and 28-35 wt % of non-sugar
solids. Blackstrap (syrup) is collected as a by-product of cane
sugar manufacture. The molasses is diluted to a mash containing ca
10-20 wt % sugar. After the pH of the mash is adjusted to about 4-5
with mineral acid, it is inoculated with the yeast, and the
fermentation is carried out non-aseptically at 20-32.degree. C. for
about 1-3 days. The fermented beer, which typically contains
approximately 6-10 wt % ethanol, is then set to the product
recovery in purification section of the plant.
Ethanol production (using 141 gallons per ton of sucrose conversion
factor) was calculated for sugarcane, sugar beets and molasses
below.
Sugarcane:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times. ##EQU00001##
.times..times..times..times. ##EQU00001.2##
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times..times..times..times..times..times..time-
s..times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times..times. ##EQU00001.3## Sugar Beets:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times. ##EQU00002##
.times..times..times..times..times..times. ##EQU00002.2##
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times..times..times..times..times..times..time-
s..times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times..times..times..times..times..times..times..times-
..times. ##EQU00002.3## Molasses:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times..times..times..times..times..times..time-
s..times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times..times..times..times..times..times..times..times-
..times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times. ##EQU00003## Raw Sugar:
.times..times..times..times..times..times..times..times..times..times.
##EQU00004##
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times. ##EQU00004.2## Refined Beet
Sugar:
.times..times..times..times..times..times..times..times..times.
##EQU00005##
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times..times. ##EQU00005.2##
Results from this study have several important implications
concerning the production of ethanol from sugar crops in the United
States. First, under existing fermentation technology, corn is
currently the cheapest feedstock available for use in the
production of ethanol in the United States. Second, given current
and future projected sugar and ethanol market prices, it appears
that the production of sugar is the most profitable use of
sugarcane or sugar beets. Third, cellulosic conversion of biomass
into ethanol offers the potential for a wide variety of feedstocks
to be used in ethanol production.
Systems and processes are described herein that can utilize these
low molecular weight to produce ethanol more rapidly and more cost
effectively.
Blends of any biomass materials described herein can be utilized
for making any of the products described herein, such as ethanol.
For example, blends of cellulosic materials and starchy materials
can be utilized for making any product described herein.
Systems for Treating Biomass
FIG. 1 shows a system 100 for converting biomass, particularly
biomass with significant cellulosic and lignocellulosic components
and/or starchy components, into useful products and co-products.
System 100 includes a feed preparation subsystem 110, a
pretreatment subsystem 114, a primary process subsystem 118, and a
post-processing subsystem 122. Feed preparation subsystem 110
receives biomass in its raw form, physically prepares the biomass
for use as feedstock by downstream processes (e.g., reduces the
size of and homogenizes the biomass), and stores the biomass both
in its raw and feedstock forms. Biomass feedstock with significant
cellulosic and/or lignocellulosic components, or starchy components
can have a high average molecular weight and crystallinity that can
make processing the feedstock into useful products (e.g.,
fermenting the feedstock to produce ethanol) difficult. For
example, others have used acids, bases and enzymes to process
cellulosic, lignocellulosic or starchy feedstocks. As described
herein, in some embodiments, such treatments are unnecessary, or
are necessary only in small or catalytic amounts.
Pretreatment subsystem 114 receives feedstock from the feed
preparation subsystem 110 and prepares the feedstock for use in
primary production processes by, for example, reducing the average
molecular weight and crystallinity of the feedstock. Primary
process subsystem 118 receives pretreated feedstock from
pretreatment subsystem 114 and produces useful products (e.g.,
ethanol, other alcohols, pharmaceuticals, and/or food products). In
some cases, the output of primary process subsystem 118 is directly
useful but, in other cases, requires further processing provided by
post-processing subsystem 122. Post-processing subsystem 122
provides further processing to product streams from primary process
system 118 which require it (e.g., distillation and denaturation of
ethanol) as well as treatment for waste streams from the other
subsystems. In some cases, the co-products of subsystems 114, 118,
122 can also be directly or indirectly useful as secondary products
and/or in increasing the overall efficiency of system 100. For
example, post-processing subsystem 122 can produce treated water to
be recycled for use as process water in other subsystems and/or can
produce burnable waste which can be used as fuel for boilers
producing steam and/or electricity.
The optimum size for biomass conversion plants is affected by
factors including economies of scale and the type and availability
of biomass used as feedstock. Increasing plant size tends to
increase economies of scale associated with plant processes.
However, increasing plant size also tends to increase the costs
(e.g., transportation costs) per unit of feedstock. Studies
analyzing these factors suggest that the appropriate size for
biomass conversion plants can range from 1000 to 10,000 or more
dried tons of feedstock per day depending at least in part on the
type of feedstock used. The type of feedstock can also impact plant
storage requirements with plants designed primarily for processing
feedstock whose availability varies seasonally (e.g., corn stover)
requiring more on- or of-site feedstock storage than plants
designed to process feedstock whose availability is relatively
steady (e.g., waste paper).
Physical Preparation
In some cases, methods of processing begin with a physical
preparation of the feedstock, e.g., size reduction of raw feedstock
materials, such as by cutting, grinding, shearing, ball milling,
nip-roll processing, or chopping. In some cases, the material can
be reduced into particles using a hammermill, disk-refiner, or
flaker. In some cases, loose feedstock (e.g., recycled paper,
starchy materials, or switchgrass) is prepared by shearing or
shredding. Screens and/or magnets can be used to remove oversized
or undesirable objects such as, for example, rocks or nails from
the feed stream.
Feed preparation systems can be configured to produce feed streams
with specific characteristics such as, for example, specific
maximum sizes, specific length-to-width, or specific surface areas
ratios. As a part of feed preparation, the bulk density of
feedstocks can be controlled (e.g., increased or decreased).
Size Reduction
In some embodiments, the material to be processed is in the form of
a fibrous material that includes fibers provided by shearing a
fiber source. For example, the shearing can be performed with a
rotary knife cutter.
For example, and by reference to FIG. 2, a fiber source 210 is
sheared, e.g., in a rotary knife cutter, to provide a first fibrous
material 212. The first fibrous material 212 is passed through a
first screen 214 having an average opening size of 1.59 mm or less
( 1/16 inch, 0.0625 inch) to provide a second fibrous material 216.
If desired, fiber source can be cut prior to the shearing, e.g.,
with a shredder. For example, when a paper is used as the fiber
source, the paper can be first cut into strips that are, e.g., 1/4-
to 1/2-inch wide, using a shredder, e.g., a counter-rotating screw
shredder, such as those manufactured by Munson (Utica, N.Y.). As an
alternative to shredding, the paper can be reduced in size by
cutting to a desired size using a guillotine cutter. For example,
the guillotine cutter can be used to cut the paper into sheets that
are, e.g., 10 inches wide by 12 inches long.
In some embodiments, the shearing of the fiber source and the
passing of the resulting first fibrous material through the first
screen are performed concurrently. The shearing and the passing can
also be performed sequentially, e.g., in a batch-type process.
For example, a rotary knife cutter can be used to concurrently
shear the fiber source and screen the first fibrous material.
Referring to FIG. 3, a rotary knife cutter 220 includes a hopper
222 that can be loaded with a shredded fiber source 224 prepared by
shredding the fiber source. Shredded fiber source is sheared
between stationary blades 230 and rotating blades 232 to provide a
first fibrous material 240. First fibrous material 240 passes
through screen 242, and the resulting second fibrous material 244
is captured in bin 250. To aid in the collection of the second
fibrous material, the bin can have a pressure below nominal
atmospheric pressure, e.g., at least 10 percent below nominal
atmospheric pressure, e.g., at least 25 percent below nominal
atmospheric pressure, at least 50 percent below nominal atmospheric
pressure, or at least 75 percent below nominal atmospheric
pressure. In some embodiments, a vacuum source 252 is utilized to
maintain the bin below nominal atmospheric pressure.
Shearing can be advantageous for "opening up," "stressing," or even
reducing the molecular weight of the fibrous materials, making the
cellulose of the materials more susceptible to chain scission
and/or reduction of crystallinity. The open materials can also be
more susceptible to oxidation when irradiated.
The fiber source can be sheared in a dry state, a hydrated state
(e.g., having up to ten percent by weight absorbed water), or in a
wet state, e.g., having between about 10 percent and about 75
percent by weight water. The fiber source can even be sheared while
partially or fully submerged under a liquid, such as water,
ethanol, or isopropanol.
The fiber source can also be sheared in a gas (such as a stream or
atmosphere of gas other than air), e.g., oxygen or nitrogen, or
steam.
Other methods of making the fibrous materials include, e.g., stone
grinding, mechanical ripping or tearing, pin grinding, ball
milling, nip-roll processing, or air attrition milling.
If desired, the fibrous materials can be separated, e.g.,
continuously or in batches, into fractions according to their
length, width, density, material type, or some combination of these
attributes.
For example, ferrous materials can be separated from any of the
fibrous materials by passing a fibrous material that includes a
ferrous material past a magnet, e.g., an electromagnet, and then
passing the resulting fibrous material through a series of screens,
each screen having different sized apertures.
The fibrous materials can also be separated, e.g., by using a high
velocity gas, e.g., air. In such an approach, the fibrous materials
are separated by drawing off different fractions, which can be
characterized photonically, if desired. Such a separation apparatus
is discussed, e.g., in Lindsey et al, U.S. Pat. No. 6,883,667.
The fibrous materials can have a low moisture content, e.g., less
than about 7.5, 5, 3, 2.5, 2, 1.5, 1, or 0.5% by weight before
processing. This material can be irradiated with a beam of
particles, such as electrons or protons. The irradiation can be
immediately following preparation of the material, or after a
moisture reduction step. e.g., drying at approximately 105.degree.
C. for 4-18 hours, so that the moisture content is, e.g., less than
about 0.5% before use.
If desired, lignin can be removed from any of the fibrous materials
that include lignin. Also, to aid in the breakdown of the materials
that include the cellulose, the material can be treated prior to
irradiation with heat, a chemical (e.g., mineral acid, base or a
strong oxidizer such as sodium hypochlorite) and/or an enzyme.
In some embodiments, the average opening size of the first screen
is less than 0.79 mm ( 1/32 inch, 0.03125 inch), e.g., less than
0.51 mm ( 1/50 inch, 0.02000 inch), less than 0.40 mm ( 1/64 inch,
0.015625 inch), less than 0.23 mm (0.009 inch), less than 0.20 mm (
1/128 inch, 0.0078125 inch), less than 0.18 mm (0.007 inch), less
than 0.13 mm (0.005 inch), or even less than less than 0.10 mm (
1/256 inch, 0.00390625 inch). The screen is prepared by
interweaving monofilaments having an appropriate diameter to give
the desired opening size. For example, the monofilaments can be
made of a metal, e.g., stainless steel. As the opening sizes get
smaller, structural demands on the monofilaments may become
greater. For example, for opening sizes less than 0.40 mm, it can
be advantageous to make the screens from monofilaments made from a
material other than stainless steel, e.g., titanium, titanium
alloys, amorphous metals, nickel, tungsten, rhodium, rhenium,
ceramics, or glass. In some embodiments, the screen is made from a
plate, e.g., a metal plate, having apertures, e.g., cut into the
plate using a laser. In some embodiments, the open area of the mesh
is less than 52%, e.g., less than 41%, less than 36%, less than
31%, less than 30%.
In some embodiments, the second fibrous material is sheared and
passed through the first screen, or a different sized screen. In
some embodiments, the second fibrous material is passed through a
second screen having an average opening size equal to or less than
that of first screen.
Referring to FIG. 4, a third fibrous material 220 can be prepared
from the second fibrous material 216 by shearing the second fibrous
material 216 and passing the resulting material through a second
screen 222 having an average opening size less than the first
screen 214.
Generally, the fibers of the fibrous materials can have a
relatively large average length-to-diameter ratio (e.g., greater
than 20-to-1), even if they have been sheared more than once. In
addition, the fibers of the fibrous materials described herein may
have a relatively narrow length and/or length-to-diameter ratio
distribution.
As used herein, average fiber widths (i.e., diameters) are those
determined optically by randomly selecting approximately 5,000
fibers. Average fiber lengths are corrected length-weighted
lengths. BET (Brunauer, Emmet and Teller) surface areas are
multi-point surface areas, and porosities are those determined by
mercury porosimetry.
The average length-to-diameter ratio of the second fibrous material
14 can be, e.g., greater than 8/1, 10/1, 15/1, 20/1, 25/1, or even
greater than 50/1. An average length of the second fibrous material
14 can be, e.g., between about 0.5 mm and 2.5 mm, e.g., between
about 0.75 mm and 1.0 mm, and an average width (i.e., diameter) of
the second fibrous material 14 can be, e.g., between about 5 .mu.m
and 50 .mu.m, e.g., between about 10 .mu.m and 30 .mu.m.
In some embodiments, a standard deviation of the length of the
second fibrous material 14 is less than 60 percent of an average
length of the second fibrous material 14, e.g., less than 50
percent of the average length, less than 40 percent of the average
length, less than 25 percent of the average length, less than 10
percent of the average length, less than 5 percent of the average
length, or even less than 1 percent of the average length.
In some embodiments, a BET surface area of the second fibrous
material is greater than 0.1 m.sup.2/g, e.g., greater than 0.25
m.sup.2/g, greater than 0.5 m.sup.2/g, greater than 1.0 m.sup.2/g,
greater than 1.5 m.sup.2/g, greater than 1.75 m.sup.2/g, greater
than 5.0 m.sup.2/g, greater than 10 m.sup.2/g, greater than 25
m.sup.2/g, greater than 35 m.sup.2/g, greater than 50 m.sup.2/g,
greater than 60 m.sup.2/g, greater than 75 m.sup.2/g, greater than
100 m.sup.2/g, greater than 150 m.sup.2/g, greater than 200
m.sup.2/g, or even greater than 250 m.sup.2/g. A porosity of the
second fibrous material 14 can be, e.g., greater than 20 percent,
greater than 25 percent, greater than 35 percent, greater than 50
percent, greater than 60 percent, greater than 70 percent, e.g.,
greater than 80 percent, greater than 85 percent, greater than 90
percent, greater than 92 percent, greater than 94 percent, greater
than 95 percent, greater than 97.5 percent, greater than 99
percent, or even greater than 99.5 percent.
In some embodiments, a ratio of the average length-to-diameter
ratio of the first fibrous material to the average
length-to-diameter ratio of the second fibrous material is, e.g.,
less than 1.5, e.g., less than 1.4, less than 1.25, less than 1.1,
less than 1.075, less than 1.05, less than 1.025, or even
substantially equal to 1.
In particular embodiments, the second fibrous material is sheared
again and the resulting fibrous material passed through a second
screen having an average opening size less than the first screen to
provide a third fibrous material. In such instances, a ratio of the
average length-to-diameter ratio of the second fibrous material to
the average length-to-diameter ratio of the third fibrous material
can be, e.g., less than 1.5, e.g., less than 1.4, less than 1.25,
or even less than 1.1.
In some embodiments, the third fibrous material is passed through a
third screen to produce a fourth fibrous material. The fourth
fibrous material can be, e.g., passed through a fourth screen to
produce a fifth material. Similar screening processes can be
repeated as many times as desired to produce the desired fibrous
material having the desired properties.
Densification
Densified materials can be processed by any of the methods
described herein, or any material described herein, e.g., any
fibrous material described herein, can be processed by any one or
more methods described herein, and then densified as described
herein.
A material, e.g., a fibrous material, having a low bulk density can
be densified to a product having a higher bulk density. For
example, a material composition having a bulk density of 0.05
g/cm.sup.3 can be densified by sealing the fibrous material in a
relatively gas impermeable structure, e.g., a bag made of
polyethylene or a bag made of alternating layers of polyethylene
and a nylon, and then evacuating the entrapped gas, e.g., air, from
the structure. After evacuation of the air from the structure, the
fibrous material can have, e.g., a bulk density of greater than 0.3
g/cm.sup.3, e.g., 0.5 g/cm.sup.3, 0.6 g/cm.sup.3, 0.7 g/cm.sup.3 or
more, e.g., 0.85 g/cm.sup.3. After densification, the product can
processed by any of the methods described herein, e.g., irradiated,
e.g., with gamma radiation. This can be advantageous when it is
desirable to transport the material to another location, e.g., a
remote manufacturing plant, where the fibrous material composition
can be added to a solution, e.g., to produce ethanol. After
piercing the substantially gas impermeable structure, the densified
fibrous material can revert to nearly its initial bulk density,
e.g., greater than 60 percent of its initial bulk density, e.g., 70
percent, 80 percent, 85 percent or more, e.g., 95 percent of its
initial bulk density. To reduce static electricity in the fibrous
material, an anti-static agent can be added to the material.
In some embodiments, the structure, e.g., bag, is formed of a
material that dissolves in a liquid, such as water. For example,
the structure can be formed from a polyvinyl alcohol so that it
dissolves when in contact with a water-based system. Such
embodiments allow densified structures to be added directly to
solutions that include a microorganism, without first releasing the
contents of the structure, e.g., by cutting.
Referring to FIG. 5, a biomass material can be combined with any
desired additives and a binder, and subsequently densified by
application of pressure, e.g., by passing the material through a
nip defined between counter-rotating pressure rolls or by passing
the material through a pellet mill. During the application of
pressure, heat can optionally be applied to aid in the
densification of the fibrous material. The densified material can
then be irradiated.
In some embodiments, the material prior to densification has a bulk
density of less than 0.25 g/cm.sup.3, e.g., 0.20 g/cm.sup.3, 0.15
g/cm.sup.3, 0.10 g/cm.sup.3, 0.05 g/cm.sup.3 or less, e.g., 0.025
g/cm.sup.3. Bulk density is determined using ASTM D1895B. Briefly,
the method involves filling a measuring cylinder of known volume
with a sample and obtaining a weight of the sample. The bulk
density is calculated by dividing the weight of the sample in grams
by the known volume of the cylinder in cubic centimeters.
The preferred binders include binders that are soluble in water,
swollen by water, or that has a glass transition temperature of
less 25.degree. C., as determined by differential scanning
calorimetry. By water-soluble binders, we mean binders having a
solubility of at least about 0.05 weight percent in water. By water
swellable binders, we mean binders that increase in volume by more
than 0.5 percent upon exposure to water.
In some embodiments, the binders that are soluble or swollen by
water include a functional group that is capable of forming a bond,
e.g., a hydrogen bond, with the fibers of the fibrous material,
e.g., cellulosic fibrous material. For example, the functional
group can be a carboxylic acid group, a carboxylate group, a
carbonyl group, e.g., of an aldehyde or a ketone, a sulfonic acid
group, a sulfonate group, a phosphoric acid group, a phosphate
group, an amide group, an amine group, a hydroxyl group, e.g., of
an alcohol, and combinations of these groups, e.g., a carboxylic
acid group and a hydroxyl group. Specific monomeric examples
include glycerin, glyoxal, ascorbic acid, urea, glycine,
pentaerythritol, a monosaccharide or a disaccharide, citric acid,
and tartaric acid. Suitable saccharides include glucose, sucrose,
lactose, ribose, fructose, mannose, arabinose and erythrose.
Polymeric examples include polyglycols, polyethylene oxide,
polycarboxylic acids, polyamides, polyamines and polysulfonic acids
polysulfonates. Specific polymeric examples include polypropylene
glycol (PPG), polyethylene glycol (PEG), polyethylene oxide, e.g.,
POLYOX.RTM., copolymers of ethylene oxide and propylene oxide,
polyacrylic acid (PAA), polyacrylamide, polypeptides,
polyethylenimine, polyvinylpyridine,
poly(sodium-4-styrenesulfonate) and
poly(2-acrylamido-methyl-1-propanesulfonic acid).
In some embodiments, the binder includes a polymer that has a glass
transition temperature less than 25.degree. C. Examples of such
polymers include thermoplastic elastomers (TPEs). Examples of TPEs
include polyether block amides, such as those available under the
tradename PEBAX.RTM., polyester elastomers, such as those available
under the tradename HYTREL.RTM., and styrenic block copolymers,
such as those available under the tradename KRATON.RTM.. Other
suitable polymers having a glass transition temperature less than
25.degree. C. include ethylene vinyl acetate copolymer (EVA),
polyolefins, e.g., polyethylene, polypropylene, ethylene-propylene
copolymers, and copolymers of ethylene and alpha olefins, e.g.,
1-octene, such as those available under the tradename ENGAGE.RTM..
In some embodiments, e.g., when the material is a fiberized
polycoated paper, the material is densified without the addition of
a separate low glass transition temperature polymer.
In a particular embodiment, the binder is a lignin, e.g., a natural
or synthetically modified lignin.
A suitable amount of binder added to the material, calculated on a
dry weight basis, is, e.g., from about 0.01 percent to about 50
percent, e.g., 0.03 percent, 0.05 percent, 0.1 percent, 0.25
percent, 0.5 percent, 1.0 percent, 5 percent, 10 percent or more,
e.g., 25 percent, based on a total weight of the densified
material. The binder can be added to the material as a neat, pure
liquid, as a liquid having the binder dissolved therein, as a dry
powder of the binder, or as pellets of the binder.
The densified fibrous material can be made in a pellet mill.
Referring to FIG. 6, a pellet mill 300 has a hopper 301 for holding
undensified material 310 that includes carbohydrate-containing
materials, such as cellulose. The hopper communicates with an auger
312 that is driven by variable speed motor 314 so that undensified
material can be transported to a conditioner 320 that stirs the
undensified material with paddles 322 that are rotated by
conditioner motor 330. Other ingredients, e.g., any of the
additives and/or fillers described herein, can be added at inlet
332. If desired, heat may be added while the fibrous material is in
the conditioner. After being conditioned, the material passes from
the conditioner through a dump chute 340, and to another auger 342.
The dump chute, as controlled by actuator 344, allows for
unobstructed passage of the material from conditioner to auger.
Auger is rotated by motor 346, and controls the feeding of the
fibrous material into die and roller assembly 350. Specifically,
the material is introduced into a hollow, cylindrical die 352,
which rotates about a horizontal axis and which has radially
extending die holes 250. Die 352 is rotated about the axis by motor
360, which includes a horsepower gauge, indicating total power
consumed by the motor. Densified material 370, e.g., in the form of
pellets, drops from chute 372 and are captured and processed, such
as by irradiation.
The material, after densification, can be conveniently in the form
of pellets or chips having a variety of shapes. The pellets can
then be irradiated. In some embodiments, the pellets or chips are
cylindrical in shape, e.g., having a maximum transverse dimension
of, e.g., 1 mm or more, e.g., 2 mm, 3 mm, 5 mm, 8 mm, 10 mm, 15 mm
or more, e.g., 25 mm. Other convenient shapes include pellets or
chips that are plate-like in form, e.g., having a thickness of 1 mm
or more, e.g., 2 mm, 3 mm, 5 mm, 8 mm, 10 mm or more, e.g., 25 mm;
a width of, e.g., 5 mm or more, e.g., 10 mm, 15 mm, 25 mm, 30 mm or
more, e.g., 50 mm; and a length of 5 mm or more, e.g., 10 mm, 15
mm, 25 mm, 30 mm or more, e.g., 50 mm.
Referring now FIG. 7A-7D, pellets can be made so that they have a
hollow inside. As shown, the hollow can be generally in-line with
the center of the pellet (FIG. 7B), or out of line with the center
of the pellet (FIG. 7C). Making the pellet hollow inside can
increase the rate of dissolution in a liquid after irradiation.
Referring now to FIG. 7D, the pellet can have, e.g., a transverse
shape that is multi-lobal, e.g., tri-lobal as shown, or
tetra-lobal, penta-lobal, hexa-lobal or deca-lobal. Making the
pellets in such transverse shapes can also increase the rate of
dissolution in a solution after irradiation.
Alternatively, the densified material can be in any other desired
form, e.g., the densified material can be in the form of a mat,
roll or bale.
EXAMPLES
In one example, half-gallon juice cartons made of un-printed white
Kraft board having a bulk density of 20 lb/ft.sup.3 can be used as
a feedstock. Cartons can be folded flat and then fed into a
shredder to produce a confetti-like material having a width of
between 0.1 inch and 0.5 inch, a length of between 0.25 inch and 1
inch and a thickness equivalent to that of the starting material
(about 0.075 inch). The confetti-like material can be fed to a
rotary knife cutter, which shears the confetti-like pieces, tearing
the pieces apart and releasing fibrous material.
In some cases, multiple shredder-shearer trains can be arranged in
series with output. In one embodiment, two shredder-shearer trains
can be arranged in series with output from the first shearer fed as
input to the second shredder. In another embodiment, three
shredder-shearer trains can be arranged in series with output from
the first shearer fed as input to the second shredder and output
from the second shearer fed as input to the third shredder.
Multiple passes through shredder-shearer trains are anticipated to
decrease particle size and increase overall surface area within the
feedstream.
In another example, fibrous material produced from shredding and
shearing juice cartons can be treated to increase its bulk density.
In some cases, the fibrous material can be sprayed with water or a
dilute stock solution of POLYOX.TM. WSR N10 (polyethylene oxide)
prepared in water. The wetted fibrous material can then be
processed through a pellet mill operating at room temperature. The
pellet mill can increase the bulk density of the feedstream by more
than an order of magnitude.
Pretreatment
Physically prepared feedstock can be pretreated for use in primary
production processes by, for example, reducing the average
molecular weight and crystallinity of the feedstock and/or
increasing the surface area and/or porosity of the feedstock.
In some embodiments, the cellulosic and/or lignocellulosic material
includes a first cellulose having a first number average molecular
weight and the resulting carbohydrate includes a second cellulose
having a second number average molecular weight lower than the
first number average molecular weight. For example, the second
number average molecular weight is lower than the first number
average molecular weight by more than about twenty-five percent,
e.g., 2.times., 3.times., 5.times., 7.times., 10.times., 25.times.,
even 100.times. reduction.
In some embodiments, the first cellulose has a first crystallinity
and the second cellulose has a second crystallinity lower than the
first crystallinity, such as lower than about two, three, five,
ten, fifteen or twenty-five percent lower.
In some embodiments, the first cellulose has a first level of
oxidation and the second cellulose has a second level of oxidation
higher than the first level of oxidation, such as two, three, four,
five, ten or even twenty-five percent higher.
Pretreatment processes can include one or more of irradiation,
sonication, oxidation, pyrolysis, and steam explosion. The various
pretreatment systems and methods can be used in combinations of
two, three, or even four of these technologies.
Pretreatment Combinations
In some embodiments, biomass can be processed by applying two or
more of any of the processes described herein, such as two, three,
four or more of radiation, sonication (or any other disruption
technique described herein, e.g., treatment with a rotor-stator
disruptor), oxidation, pyrolysis, and steam explosion either with
or without prior, intermediate, or subsequent feedstock preparation
as described herein. The processes can be applied to the biomass in
any order or concurrently For example, a carbohydrate can be
prepared by applying radiation, sonication, oxidation, pyrolysis,
and, optionally, steam explosion to a cellulosic and/or
lignocellulosic material (in any order or concurrently). The
provided carbohydrate-containing material can then be converted by
one or more microorganisms, such as bacteria, yeast, or mixtures of
yeast and bacteria, to a number of desirable products, as described
herein. Multiple processes can provide materials that can be more
readily utilized by a variety of microorganisms because of their
lower molecular weight, lower crystallinity, and/or enhanced
solubility. Multiple processes can provide synergies and can reduce
overall energy input required in comparison to any single
process.
For example, in some embodiments, feedstocks are provided that
include a carbohydrate that is produced by a process that includes
irradiating and sonicating, irradiating and oxidizing, irradiating
and pyrolyzing, or irradiating and steam-exploding (in either order
or concurrently) a cellulosic and/or a lignocellulosic material.
The provided feedstock can then be contacted with a microorganism
having the ability to convert at least a portion, e.g., at least
about 1 percent by weight, of the feedstock to the product, such as
the combustible fuel.
Pretreatment Conditions
In some embodiments, the process does not include hydrolyzing the
cellulosic and/or lignocellulosic material, such as with an acid,
e.g., a mineral acid, such as hydrochloric or sulfuric acid, an
enzyme or a base. If desired, some or none of the feedstock can
include a hydrolyzed material. For example, in some embodiments, at
least about seventy percent by weight of the feedstock is an
unhydrolyzed material, e.g., at least at 95 percent by weight of
the feedstock is an unhydrolyzed material. In some embodiments,
substantially all of the feedstock is an unhydrolyzed material. For
example, treatment with alkali can be avoided.
Any feedstock or any reactor or fermentor charged with a feedstock
can include a buffer, such as sodium bicarbonate, ammonium chloride
or Tris; an electrolyte, such as potassium chloride, sodium
chloride, or calcium chloride; a growth factor, such as biotin
and/or a base pair such as uracil or an equivalent thereof; a
surfactant, such as Tween.RTM. or polyethylene glycol; a mineral,
such as such as calcium, chromium, copper, iodine, iron, selenium,
or zinc; or a chelating agent, such as ethylene diamine, ethylene
diamine tetraacetic acid (EDTA) (or its salt form, e.g., sodium or
potassium EDTA), or dimercaprol.
When radiation is utilized, it can be applied to any sample that is
dry or wet, or even dispersed in a liquid, such as water. For
example, irradiation can be performed on cellulosic and/or
lignocellulosic material in which less than about 25 percent by
weight of the cellulosic and/or lignocellulosic material has
surfaces wetted with a liquid, such as water. In some embodiments,
irradiating is performed on cellulosic and/or lignocellulosic
material in which substantially none of the cellulosic and/or
lignocellulosic material is wetted with a liquid, such as
water.
In some embodiments, any processing described herein occurs with
the cellulosic and/or lignocellulosic material remaining dry as
acquired or after the material has been dried, e.g., using heat
and/or reduced pressure. For example, in some embodiments, the
cellulosic and/or lignocellulosic material has less than about five
percent by weight retained water, measured at 25.degree. C. and at
fifty percent relative humidity.
The feedstock can be treated so that it has a low moisture content,
e.g., less than about 7.5, 5, 3, 2.5, 2, 1.5, 1, or 0.5% by weight.
This material can be irradiated with a beam of particles, such as
electrons or protons. The irradiation can be immediately following
preparation of the material or after a moisture reduction step,
e.g., drying at approximately 105.degree. C. for 4-18 hours.
If desired, a swelling agent, as defined herein, can be utilized in
any process described herein. In some embodiments, when a
cellulosic and/or lignocellulosic material is processed using
radiation, less than about 25 percent by weight of the cellulosic
and/or lignocellulosic material is in a swollen state, the swollen
state being characterized as having a volume of more than about 2.5
percent higher than an unswollen state, e.g., more than 5.0, 7.5,
10, or 15 percent higher than the unswollen state. In specific
embodiments when radiation is utilized, the cellulosic and/or
lignocellulosic material includes a swelling agent, and swollen
cellulosic and/or lignocellulosic receives a dose of less than
about 10 Mrad. In other embodiments, when radiation is utilized on
a cellulosic and/or lignocellulosic material, substantially none of
the cellulosic and/or lignocellulosic material is in a swollen
state.
In some embodiments, no chemicals, e.g., no swelling agents, are
added to the biomass prior to irradiation. For example, in some of
these embodiments no alkaline substances (such as sodium hydroxide,
potassium hydroxide, lithium hydroxide and ammonium hydroxides),
acidifying agents (such as mineral acids (e.g., sulfuric acid,
hydrochloric acid and phosphoric acid)), salts, such as zinc
chloride, calcium carbonate, sodium carbonate,
benzyltrimethylammonium sulfate, or basic organic amines, such as
ethylene diamine, are added prior to irradiation or other
processing. In some cases, no additional water is added. For
example, the biomass prior to processing can have less than 0.5
percent by weight added chemicals, e.g., less than 0.4, 0.25, 0.15
or 0.1 percent by weight added chemicals. In some instances, the
biomass has no more than a trace, e.g., less than 0.05 percent by
weight added chemicals, prior to irradiation. In other instances,
the biomass prior to irradiation has substantially no added
chemicals or swelling agents. Avoiding the use of such chemicals
can also be extended throughout processing, e.g., at all times
prior to fermentation, or at all times.
When radiation is utilized in any process, it can be applied while
the cellulosic and/or lignocellulosic is exposed to air,
oxygen-enriched air, or even oxygen itself, or blanketed by an
inert gas such as nitrogen, argon, or helium. When maximum
oxidation is desired, an oxidizing environment is utilized, such as
air or oxygen. The distance from the radiation source can also be
optimized to maximize reactive gas formation, e.g., ozone and/or
oxides of nitrogen.
When radiation is utilized, it may be applied to biomass, such as
cellulosic and/or lignocellulosic material, under a pressure of
greater than about 2.5 atmospheres, such as greater than 5, 10, 15,
20 or even greater than about 50 atmospheres.
When the process includes radiation, the irradiating can be
performed utilizing an ionizing radiation, such as gamma rays,
x-rays, energetic ultraviolet radiation, such as ultraviolet C
radiation having a wavelength of from about 100 nm to about 280 nm,
a beam of particles, such as a beam of electrons, slow neutrons or
alpha particles. In some embodiments, irradiating includes two or
more radiation sources, such as gamma rays and a beam of electrons,
which can be applied in either order or concurrently.
Any processing technique described herein can be used at a pressure
above or below normal, earth-bound atmospheric pressure. For
example, any process that utilizes radiation, sonication,
oxidation, pyrolysis, steam explosion, or combinations of any of
these processes to provide materials that include a carbohydrate
can be performed under high pressure, which can increase reaction
rates. For example, any process or combination of processes can be
performed at a pressure greater than about normal atmospheric
pressure, e.g., at a pressure of greater than about 25 MPa, e.g.,
greater than 50 MPa, 75 MPa, 100 MPa, 150 MPa, 200 MPa, 250 MPa,
350 MPa, 500 MPa, 750 MPa, 1,000 MPa, or greater than 1,500
MPa.
Radiation Treatment
One or more irradiation processing sequences can be used to process
raw feedstock from a wide variety of different sources to extract
useful substances from the feedstock, and to provide partially
degraded organic material which functions as input to further
processing steps and/or sequences. Irradiation can reduce the
molecular weight and/or crystallinity of feedstock. In some
embodiments, energy deposited in a material that releases an
electron from its atomic orbital is used to irradiate the
materials. The radiation may be provided by 1) heavy charged
particles, such as alpha particles or protons, 2) electrons,
produced, for example, in beta decay or electron beam accelerators,
or 3) electromagnetic radiation, for example, gamma rays, x rays,
or ultraviolet rays. In one approach, radiation produced by
radioactive substances can be used to irradiate the feedstock. In
some embodiments, any combination in any order or concurrently of
(1) through (3) may be utilized. In another approach,
electromagnetic radiation (e.g., produced using electron beam
emitters) can be used to irradiate the feedstock. The doses applied
depend on the desired effect and the particular feedstock. For
example, high doses of radiation can break chemical bonds within
feedstock components and low doses of radiation can increase
chemical bonding (e.g., cross-linking) within feedstock components.
In some instances when chain scission is desirable and/or polymer
chain functionalization is desirable, particles heavier than
electrons, such as protons, helium nuclei, argon ions, silicon
ions, neon ions carbon ions, phosphorus ions, oxygen ions or
nitrogen ions can be utilized. When ring-opening chain scission is
desired, positively charged particles can be utilized for their
Lewis acid properties for enhanced ring-opening chain scission. For
example, when oxygen-containing functional groups are desired,
irradiation in the presence of oxygen or even irradiation with
oxygen ions can be performed. For example, when nitrogen-containing
functional groups are desirable, irradiation in the presence of
nitrogen or even irradiation with nitrogen ions can be
performed.
Referring to FIG. 8, in one method, a first material 2 that is or
includes cellulose having a first number average molecular weight
(.sup.TM.sub.N1) is irradiated, e.g., by treatment with ionizing
radiation (e.g., in the form of gamma radiation, X-ray radiation,
100 nm to 280 nm ultraviolet (UV) light, a beam of electrons or
other charged particles) to provide a second material 3 that
includes cellulose having a second number average molecular weight
(.sup.TM.sub.N2) lower than the first number average molecular
weight. The second material (or the first and second material) can
be combined with a microorganism (e.g., a bacterium or a yeast)
that can utilize the second and/or first material to produce a
product, e.g., a fuel 5 that is or includes hydrogen, an alcohol
(e.g., ethanol or butanol, such as n-, sec- or t-butanol), an
organic acid, a hydrocarbon or mixtures of any of these.
Since the second material 3 has cellulose having a reduced
molecular weight relative to the first material, and in some
instances, a reduced crystallinity as well, the second material is
generally more dispersible, swellable and/or soluble in a solution
containing a microorganism. These properties make the second
material 3 more susceptible to chemical, enzymatic and/or
biological attack relative to the first material 2, which can
greatly improve the production rate and/or production level of a
desired product, e.g., ethanol. Radiation can also sterilize the
materials.
In some embodiments, the second number average molecular weight
(M.sub.N2) is lower than the first number average molecular weight
(.sup.TM.sub.N1) by more than about 10 percent, e.g., 15, 20, 25,
30, 35, 40, 50 percent, 60 percent, or even more than about 75
percent.
In some instances, the second material has cellulose that has as
crystallinity (.sup.TC.sub.2) that is lower than the crystallinity
(.sup.TC.sub.1) of the cellulose of the first material. For
example, (.sup.TC.sub.2) can be lower than (.sup.TC.sub.1) by more
than about 10 percent, e.g., 15, 20, 25, 30, 35, 40, or even more
than about 50 percent.
In some embodiments, the starting crystallinity index (prior to
irradiation) is from about 40 to about 87.5 percent, e.g., from
about 50 to about 75 percent or from about 60 to about 70 percent,
and the crystallinity index after irradiation is from about 10 to
about 50 percent, e.g., from about 15 to about 45 percent or from
about 20 to about 40 percent. However, in some embodiments, e.g.,
after extensive irradiation, it is possible to have a crystallinity
index of lower than 5 percent. In some embodiments, the material
after irradiation is substantially amorphous.
In some embodiments, the starting number average molecular weight
(prior to irradiation) is from about 200,000 to about 3,200,000,
e.g., from about 250,000 to about 1,000,000 or from about 250,000
to about 700,000, and the number average molecular weight after
irradiation is from about 50,000 to about 200,000, e.g., from about
60,000 to about 150,000 or from about 70,000 to about 125,000.
However, in some embodiments, e.g., after extensive irradiation, it
is possible to have a number average molecular weight of less than
about 10,000 or even less than about 5,000.
In some embodiments, the second material can have a level of
oxidation (.sup.TO.sub.2) that is higher than the level of
oxidation (.sup.TO.sub.1) of the first material. A higher level of
oxidation of the material can aid in its dispersibility,
swellability and/or solubility, further enhancing the materials
susceptibility to chemical, enzymatic or biological attack. In some
embodiments, to increase the level of the oxidation of the second
material relative to the first material, the irradiation is
performed under an oxidizing environment, e.g., under a blanket of
air or oxygen, producing a second material that is more oxidized
than the first material. For example, the second material can have
more hydroxyl groups, aldehyde groups, ketone groups, ester groups
or carboxylic acid groups, which can increase its
hydrophilicity.
Ionizing Radiation
Each form of radiation ionizes the biomass via particular
interactions, as determined by the energy of the radiation. Heavy
charged particles primarily ionize matter via Coulomb scattering;
furthermore, these interactions produce energetic electrons that
may further ionize matter. Alpha particles are identical to the
nucleus of a helium atom and are produced by the alpha decay of
various radioactive nuclei, such as isotopes of bismuth, polonium,
astatine, radon, francium, radium, several actinides, such as
actinium, thorium, uranium, neptunium, curium, californium,
americium, and plutonium.
When particles are utilized, they can be neutral (uncharged),
positively charged or negatively charged. When charged, the charged
particles can bear a single positive or negative charge, or
multiple charges, e.g., one, two, three or even four or more
charges. In instances in which chain scission is desired,
positively charged particles may be desirable, in part, due to
their acidic nature. When particles are utilized, the particles can
have the mass of a resting electron, or greater, e.g., 500, 1000,
1500, or 2000 or more times the mass of a resting electron. For
example, the particles can have a mass of from about 1 atomic unit
to about 150 atomic units, e.g., from about 1 atomic unit to about
50 atomic units, or from about 1 to about 25, e.g., 1, 2, 3, 4, 5,
10, 12 or 15 amu. Accelerators used to accelerate the particles can
be electrostatic DC, electrodynamic DC, RF linear, magnetic
induction linear or continuous wave. For example, cyclotron type
accelerators are available from IBA, Belgium, such as the
Rhodotron.RTM. system, while DC type accelerators are available
from RDI, now IBA Industrial, such as the Dynamitron.RTM.. Ions and
ion accelerators are discussed in Introductory Nuclear Physics,
Kenneth S. Krane, John Wiley & Sons, Inc. (1988), Krsto Prelec,
FIZIKA B 6 (1997) 4, 177-206, a copy of which is attached hereto as
Appendix B, Chu, William T., "Overview of Light-Ion Beam Therapy",
Columbus-Ohio, ICRU-IAEA Meeting, 18-20 Mar. 2006, a copy of which
is attached hereto as Appendix C, Iwata, Y. et al.,
"Alternating-Phase-Focused IH-DTL for Heavy-Ion Medical
Accelerators", Proceedings of EPAC 2006, Edinburgh, Scotland, a
copy of which is attached hereto as Appendix D, and Leitner, C. M.
et al., "Status of the Superconducting ECR Ion Source Venus",
Proceedings of EPAC 2000, Vienna, Austria, a copy of which is
attached hereto as Appendix E.
Electrons interact via Coulomb scattering and bremsstrahlung
radiation produced by changes in the velocity of electrons.
Electrons may be produced by radioactive nuclei that undergo beta
decay, such as isotopes of iodine, cesium, technetium, and iridium.
Alternatively, an electron gun can be used as an electron source
via thermionic emission.
Electromagnetic radiation interacts via three processes:
photoelectric absorption, Compton scattering, and pair production.
The dominating interaction is determined by the energy of the
incident radiation and the atomic number of the material. The
summation of interactions contributing to the absorbed radiation in
cellulosic material can be expressed by the mass absorption
coefficient.
Electromagnetic radiation is subclassified as gamma rays, x rays,
ultraviolet rays, infrared rays, microwaves, or radiowaves,
depending on its wavelength.
For example, gamma radiation can be employed to irradiate the
materials. Referring to FIGS. 9 and 10 (an enlarged view of region
R), a gamma irradiator 10 includes gamma radiation sources 408,
e.g., pellets, a working table 14 for holding the materials to be
irradiated and storage 16, e.g., made of a plurality iron plates,
all of which are housed in a concrete containment chamber (vault)
20 that includes a maze entranceway 22 beyond a lead-lined door 26.
Storage 16 includes a plurality of channels 30, e.g., sixteen or
more channels, allowing the gamma radiation sources to pass through
storage on their way proximate the working table.
In operation, the sample to be irradiated is placed on a working
table. The irradiator is configured to deliver the desired dose
rate and monitoring equipment is connected to an experimental block
31. The operator then leaves the containment chamber, passing
through the maze entranceway and through the lead-lined door. The
operator mans a control panel 32, instructing a computer 33 to lift
the radiation sources 12 into working position using cylinder 36
attached to a hydraulic pump 40.
Gamma radiation has the advantage of a significant penetration
depth into a variety of material in the sample. Sources of gamma
rays include radioactive nuclei, such as isotopes of cobalt,
calcium, technicium, chromium, gallium, indium, iodine, iron,
krypton, samarium, selenium, sodium, thalium, and xenon.
Sources of x rays include electron beam collision with metal
targets, such as tungsten or molybdenum or alloys, or compact light
sources, such as those produced commercially by Lyncean.
Sources for ultraviolet radiation include deuterium or cadmium
lamps.
Sources for infrared radiation include sapphire, zinc, or selenide
window ceramic lamps.
Sources for microwaves include klystrons, Slevin type RF sources,
or atom beam sources that employ hydrogen, oxygen, or nitrogen
gases.
Various other irradiating devices may be used in the methods
disclosed herein, including field ionization sources, electrostatic
ion separators, field ionization generators, thermionic emission
sources, microwave discharge ion sources, recirculating or static
accelerators, dynamic linear accelerators, van de Graaff
accelerators, and folded tandem accelerators. Such devices are
disclosed, for example, in U.S. Provisional Application Ser. No.
61/073,665, the complete disclosure of which is incorporated herein
by reference.
Electron Beam
In some embodiments, a beam of electrons is used as the radiation
source. A beam of electrons has the advantages of high dose rates
(e.g., 1, 5, or even 10 Mrad per second), high throughput, less
containment, and less confinement equipment. Electron beams can
also have up to 80 percent electrical efficiency, allowing for a
low energy usage, which can translate into a low cost of operation
and low greenhouse gas emissions corresponding to the small amount
of energy used. Electrons can also be more efficient at causing
chain scission. In addition, electrons having energies of 4-10 MeV
can have a penetration depth of 5 to 30 mm or more, such as 40 mm.
In low bulk density materials, such as many of the materials
described herein, e.g., materials having a bulk density of less
than about 0.5 g/cm.sup.3, electrons having energies in the 4-10
MeV range can penetrate 4-8 inches or even more.
Electron beams can be generated, e.g., by electrostatic generators,
cascade generators, transformer generators, low energy accelerators
with a scanning system, low energy accelerators with a linear
cathode, linear accelerators, and pulsed accelerators. Electrons as
an ionizing radiation source can be useful, e.g., for relatively
thin piles of materials, e.g., less than 0.5 inch, e.g., less than
0.4 inch, 0.3 inch, 0.2 inch, or less than 0.1 inch. In some
embodiments, the energy of each electron of the electron beam is
from about 0.3 MeV to about 2.0 MeV (million electron volts), e.g.,
from about 0.5 MeV to about 1.5 MeV, or from about 0.7 MeV to about
1.25 MeV.
FIG. 11 shows a process flow diagram 3000 that includes various
steps in an electron beam irradiation feedstock pretreatment
sequence. In first step 3010, a supply of dry feedstock is received
from a feed source. As discussed above, the dry feedstock from the
feed source may be pre-processed prior to delivery to the electron
beam irradiation devices. For example, if the feedstock is derived
from plant sources, certain portions of the plant material may be
removed prior to collection of the plant material and/or before the
plant material is delivered by the feedstock transport device.
Alternatively, or in addition, as expressed in optional step 3020,
the biomass feedstock can be subjected to mechanical processing
(e.g., to reduce the average length of fibers in the feedstock)
prior to delivery to the electron beam irradiation devices.
In step 3030, the dry feedstock is transferred to a feedstock
transport device (e.g., a conveyor belt) and is distributed over
the cross-sectional width of the feedstock transport device
approximately uniformly by volume. This can be accomplished, for
example, manually or by inducing a localized vibration motion at
some point in the feedstock transport device prior to the electron
beam irradiation processing.
In some embodiments, a mixing system introduces a chemical agent
3045 into the feedstock in an optional process 3040 that produces a
slurry. Combining water with the processed feedstock in mixing step
3040 creates an aqueous feedstock slurry that may be transported
through, for example, piping rather than using, for example, a
conveyor belt.
The next step 3050 is a loop that encompasses exposing the
feedstock (in dry or slurry form) to electron beam radiation via
one or more (say, N) electron beam irradiation devices. The
feedstock slurry is moved through each of the N "showers" of
electron beams at step 3052. The movement may either be at a
continuous speed through and between the showers, or there may be a
pause through each shower, followed by a sudden movement to the
next shower. A small slice of the feedstock slurry is exposed to
each shower for some predetermined exposure time at step 3053.
Electron beam irradiation devices may be procured commercially from
Ion Beam Applications, Louvain-la-Neuve, Belgium or the Titan
Corporation, San Diego, Calif. Typical electron energies can be 1
MeV, 2 MeV, 4.5 MeV, 7.5 MeV, or 10 MeV. Typical electron beam
irradiation device power can be 1 kW, 5 kW, 10 kW, 20 kW, 50 kW,
100 kW, 250 kW, or 500 kW. Effectiveness of depolymerization of the
feedstock slurry depends on the electron energy used and the dose
applied, while exposure time depends on the power and dose. Typical
doses may take values of 1 kGy, 5 kGy, 10 kGy, 20 kGy, 50 kGy, 100
kGy, or 200 kGy.
Tradeoffs in considering electron beam irradiation device power
specifications include cost to operate, capital costs,
depreciation, and device footprint. Tradeoffs in considering
exposure dose levels of electron beam irradiation would be energy
costs and environment, safety, and health (ESH) concerns.
Typically, generators are housed in a vault, e.g., of lead or
concrete. Tradeoffs in considering electron energies include energy
costs; here, a lower electron energy may be advantageous in
encouraging depolymerization of certain feedstock slurry (see, for
example, Bouchard, et al, Cellulose (2006) 13: 601-610).
It may be advantageous to provide a double-pass of electron beam
irradiation in order to provide a more effective depolymerization
process. For example, the feedstock transport device could direct
the feedstock (in dry or slurry form) underneath and in a reverse
direction to its initial transport direction. Double-pass systems
can allow thicker feedstock slurries to be processed and can
provide a more uniform depolymerization through the thickness of
the feedstock slurry.
The electron beam irradiation device can produce either a fixed
beam or a scanning beam. A scanning beam may be advantageous with
large scan sweep length and high scan speeds, as this would
effectively replace a large, fixed beam width. Further, available
sweep widths of 0.5 m, 1 m, 2 m or more are available.
Once a portion of feedstock slurry has been transported through the
N electron beam irradiation devices, it may be necessary in some
embodiments, as in step 3060, to mechanically separate the liquid
and solid components of the feedstock slurry. In these embodiments,
a liquid portion of the feedstock slurry is filtered for residual
solid particles and recycled back to the slurry preparation step
3040. A solid portion of the feedstock slurry is then advanced on
to the next processing step 3070 via the feedstock transport
device. In other embodiments, the feedstock is maintained in slurry
form for further processing.
Heavy Ion Particle Beams
Particles heavier than electrons can be utilized to irradiate
carbohydrates or materials that include carbohydrates, e.g.,
cellulosic materials, lignocellulosic materials, starchy materials,
or mixtures of any of these and others described herein. For
example, protons, helium nuclei, argon ions, silicon ions, neon
ions carbon ions, phosphorus ions, oxygen ions or nitrogen ions can
be utilized. In some embodiments, particles heavier than electrons
can induce higher amounts of chain scission. In some instances,
positively charged particles can induce higher amounts of chain
scission than negatively charged particles due to their
acidity.
Heavier particle beams can be generated, e.g., using linear
accelerators or cyclotrons. In some embodiments, the energy of each
particle of the beam is from about 1.0 MeV/atomic unit to about
6,000 MeV/atomic unit, e.g., from about 3 MeV/atomic unit to about
4,800 MeV/atomic unit, or from about 10 MeV/atomic unit to about
1,000 MeV/atomic unit.
Electromagnetic Radiation
In embodiments in which the irradiating is performed with
electromagnetic radiation, the electromagnetic radiation can have,
e.g., energy per photon (in electron volts) of greater than
10.sup.2 eV, e.g., greater than 10.sup.3, 10.sup.4, 10.sup.5,
10.sup.6, or even greater than 10.sup.7 eV. In some embodiments,
the electromagnetic radiation has energy per photon of between
10.sup.4 and 10.sup.7, e.g., between 10.sup.5 and 10.sup.6 eV. The
electromagnetic radiation can have a frequency of, e.g., greater
than 10.sup.16 hz, greater than 10'' hz, 10.sup.18, 10.sup.19,
1020, or even greater than 10.sup.21 hz. In some embodiments, the
electromagnetic radiation has a frequency of between 10.sup.18 and
10.sup.22 hz, e.g., between 10.sup.19 to 10.sup.21 hz.
Doses
In some embodiments, the irradiating (with any radiation source or
a combination of sources) is performed until the material receives
a dose of at least 0.05 Mrad, e.g., at least 0.1, 0.25, 1.0, 2.5,
5.0, or 10.0 Mrad. In some embodiments, the irradiating is
performed until the material receives a dose of between 1.0 Mrad
and 6.0 Mrad, e.g., between 1.5 Mrad and 4.0 Mrad. In other
embodiments, irradiating is performed at a dose between about 0.1
MRad and about 10 MRad, e.g., between about 0.25 MRad and about 9
MRad, between about 0.5 MRad and about 7.5 MRad or between about
0.75 MRad and about 5 MRad.
In some embodiments, the irradiating is performed at a dose rate of
between 5.0 and 1500.0 kilorads/hour, e.g., between 10.0 and 750.0
kilorads/hour or between 50.0 and 350.0 kilorads/hours.
In some embodiments, two or more radiation sources are used, such
as two or more ionizing radiations. For example, samples can be
treated, in any order, with a beam of electrons, followed by gamma
radiation and UV light having wavelengths from about 100 nm to
about 280 nm. In some embodiments, samples are treated with three
ionizing radiation sources, such as a beam of electrons, gamma
radiation, and energetic UV light.
In one example of the use of radiation as a pretreatment,
half-gallon juice cartons made of un-printed polycoated white Kraft
board having a bulk density of 20 lb/ft.sup.3 are used as a
feedstock. Cartons are folded flat and then fed into a sequence of
three shredder-shearer trains arranged in series with output from
the first shearer fed as input to the second shredder, and output
from the second shearer fed as input to the third shredder. The
fibrous material produced by the shredder-shearer train can be
sprayed with water and processed through a pellet mill operating at
room temperature. The densified pellets can be placed in a glass
ampoule which is evacuated under high vacuum and then back-filled
with argon gas. The ampoule is sealed under argon. Alternatively,
in another example, the ampoule is sealed under an atmosphere of
air. The pellets in the ampoule are irradiated with gamma radiation
for about 3 hours at a dose rate of about 1 Mrad per hour to
provide an irradiated material in which the cellulose has a lower
molecular weight than the starting material.
Additives to Enhance Molecular Weight Breakdown During
Irradiation
In some embodiments, prior to irradiation, various materials, e.g.,
solids or liquids, can be added to the biomass to enhance molecular
weight reduction. In those instances in which a liquid is utilized,
the liquid can be in contact with outer surfaces of the biomass
and/or the liquid can be in interior portions of the biomass, e.g.,
infused into the biomass.
For example, the material can be a neutral weak base, such as
alanine, ammonia, ammonia/water mixture, e.g., 25 percent by weight
ammonia in water, water, methyl amine, dimethyl amine, trimethyl
amine, pyridine, or a anionic base, such as a salt of acetic acid
(e.g., sodium acetate), sodium carbonate, sodium bicarbonate or a
salt of an ion of hydrogen sulfide (e.g., sodium hydrosulfide).
Alternatively, the material can be a neutral weak acid, such as
formic acid, acetic acid, trichloroacetic acid, water, hydrogen
sulfide or a cationic acid, such as an ammonium salt.
Quenching and Controlled Functionalization of Biomass
After treatment with one or more ionizing radiations, such as
photonic radiation (e.g., X-rays or gamma-rays), e-beam radiation
or particles heavier than electrons that are positively or
negatively charged (e.g., protons or carbon ions), any of the
carbohydrate-containing materials or mixtures described herein
become ionized; that is, they include radicals at levels that are
detectable with an electron spin resonance spectrometer. The
current limit of detection of the radicals is about 10.sup.14 spins
at room temperature. After ionization, any biomass material that
has been ionized can be quenched to reduce the level of radicals in
the ionized biomass, e.g., such that the radicals are no longer
detectable with the electron spin resonance spectrometer. For
example, the radicals can be quenched by the application of a
sufficient pressure to the biomass and/or by utilizing a fluid in
contact with the ionized biomass, such as a gas or liquid, that
reacts with (quenches) the radicals. Using a gas or liquid to at
least aid in the quenching of the radicals can be used to
functionalize the ionized biomass with a desired amount and kind of
functional groups, such as carboxylic acid groups, enol groups,
aldehyde groups, nitro groups, nitrile groups, amino groups, alkyl
amino groups, alkyl groups, chloroalkyl groups or chlorofluoroalkyl
groups. In some instances, such quenching can improve the stability
of some of the ionized biomass materials. For example, quenching
can improve the resistance of the biomass to oxidation.
Functionalization by quenching can also improve the solubility of
any biomass described herein, can improve its thermal stability,
and can improve material utilization by various microorganisms. For
example, the functional groups imparted to the biomass material by
the quenching can act as receptor sites for attachment by
microorganisms, e.g., to enhance cellulose hydrolysis by various
microorganisms.
FIG. 11A illustrates changing a molecular and/or a supramolecular
structure of a biomass feedstock by pretreating the biomass
feedstock with ionizing radiation, such as with electrons or ions
of sufficient energy to ionize the biomass feedstock, to provide a
first level of radicals. As shown in FIG. 11A, if ionized biomass
remains in the atmosphere, it will be oxidized, such as to an
extent that carboxylic acid groups are generated by reacting with
the atmospheric oxygen. In some instances with some materials, such
oxidation is desired because it can aid in the further breakdown in
molecular weight of the carbohydrate-containing biomass, and the
oxidation groups, e.g., carboxylic acid groups can be helpful for
solubility and microorganism utilization in some instances.
However, since the radicals can "live" for some time after
irradiation, e.g., longer than 1 day, 5 days, 30 days, 3 months, 6
months or even longer than 1 year, materials properties can
continue to change over time, which in some instances, can be
undesirable. Detecting radicals in irradiated samples by electron
spin resonance spectroscopy and radical lifetimes in such samples
is discussed in Bartolotta et al., Physics in Medicine and Biology,
46 (2001), 461-471 and in Bartolotta et al., Radiation Protection
Dosimetry, Vol. 84, Nos. 1-4, pp. 293-296 (1999) which are attached
hereto as Appendix F and Appendix G, respectively. As shown in FIG.
11A, the ionized biomass can be quenched to functionalize and/or to
stabilize the ionized biomass. At any point, e.g., when the
material is "alive", "partially alive" or fully quenched, the
pretreated biomass can be converted into a product, e.g., a fuel, a
food, or a composite.
In some embodiments, the quenching includes an application of
pressure to the biomass, such as by mechanically deforming the
biomass, e.g., directly mechanically compressing the biomass in
one, two, or three dimensions, or applying pressure to a fluid in
which the biomass is immersed, e.g., isostatic pressing. In such
instances, the deformation of the material itself brings radicals,
which are often trapped in crystalline domains, in close enough
proximity so that the radicals can recombine, or react with another
group. In some instances, the pressure is applied together with the
application of heat, such as a sufficient quantity of heat to
elevate the temperature of the biomass to above a melting point or
softening point of a component of the biomass, such as lignin,
cellulose or hemicellulose. Heat can improve molecular mobility in
the polymeric material, which can aid in the quenching of the
radicals. When pressure is utilized to quench, the pressure can be
greater than about 1000 psi, such as greater than about 1250 psi,
1450 psi, 3625 psi, 5075 psi, 7250 psi, 10000 psi or even greater
than 15000 psi.
In some embodiments, quenching includes contacting the biomass with
a fluid, such as a liquid or gas, e.g., a gas capable of reacting
with the radicals, such as acetylene or a mixture of acetylene in
nitrogen, ethylene, chlorinated ethylenes or chlorofluoroethylenes,
propylene or mixtures of these gases. In other particular
embodiments, quenching includes contacting the biomass with a
liquid, e.g., a liquid soluble in, or at least capable of
penetrating into the biomass and reacting with the radicals, such
as a diene, such as 1,5-cyclooctadiene. In some specific
embodiments, the quenching includes contacting the biomass with an
antioxidant, such as Vitamin E. If desired, the biomass feedstock
can include an antioxidant dispersed therein, and the quenching can
come from contacting the antioxidant dispersed in the biomass
feedstock with the radicals.
Other methods for quenching are possible. For example, any method
for quenching radicals in polymeric materials described in
Muratoglu et al., U.S. Patent Application Publication No.
2008/0067724 and Muratoglu et al., U.S. Pat. No. 7,166,650, which
are attached as Appendix H and Appendix I, respectively, can be
utilized for quenching any ionized biomass material described
herein. Furthermore any quenching agent (described as a
"sensitizing agent" in the above-noted Muratoglu disclosures)
and/or any antioxidant described in either Muratoglu reference can
be utilized to quench any ionized biomass material.
Functionalization can be enhanced by utilizing heavy charged ions,
such as any of the heavier ions described herein. For example, if
it is desired to enhance oxidation, charged oxygen ions can be
utilized for the irradiation. If nitrogen functional groups are
desired, nitrogen ions or anions that includes nitrogen can be
utilized. Likewise, if sulfur or phosphorus groups are desired,
sulfur or phosphorus ions can be used in the irradiation.
In some embodiments, after quenching any of the quenched ionized
materials described herein can be further treated with one or more
of radiation, such as ionizing or non-ionizing radiation,
sonication, pyrolysis, and oxidation for additional molecular
and/or supramolecular structure change.
Particle Beam Exposure in Fluids
In some cases, the cellulosic or lignocellulosic materials can be
exposed to a particle beam in the presence of one or more
additional fluids (e.g., gases and/or liquids). Exposure of a
material to a particle beam in the presence of one or more
additional fluids can increase the efficiency of the treatment.
In some embodiments, the material is exposed to a particle beam in
the presence of a fluid such as air. Particles accelerated in any
one or more of the types of accelerators disclosed herein (or
another type of accelerator) are coupled out of the accelerator via
an output port (e.g., a thin membrane such as a metal foil), pass
through a volume of space occupied by the fluid, and are then
incident on the material. In addition to directly treating the
material, some of the particles generate additional chemical
species by interacting with fluid particles (e.g., ions and/or
radicals generated from various constituents of air, such as ozone
and oxides of nitrogen). These generated chemical species can also
interact with the material, and can act as initiators for a variety
of different chemical bond-breaking reactions in the material. For
example, any oxidant produced can oxidize the material, which can
result in molecular weight reduction.
In certain embodiments, additional fluids can be selectively
introduced into the path of a particle beam before the beam is
incident on the material. As discussed above, reactions between the
particles of the beam and the particles of the introduced fluids
can generate additional chemical species, which react with the
material and can assist in functionalizing the material, and/or
otherwise selectively altering certain properties of the material.
The one or more additional fluids can be directed into the path of
the beam from a supply tube, for example. The direction and flow
rate of the fluid(s) that is/are introduced can be selected
according to a desired exposure rate and/or direction to control
the efficiency of the overall treatment, including effects that
result from both particle-based treatment and effects that are due
to the interaction of dynamically generated species from the
introduced fluid with the material. In addition to air, exemplary
fluids that can be introduced into the ion beam include oxygen,
nitrogen, one or more noble gases, one or more halogens, and
hydrogen.
Irradiating Low Bulk Density Biomass Materials and Cooling
Irradiated Biomass
During treatment of biomass materials with ionizing radiation,
especially at high dose rates, such as at rates greater then 0.15
Mrad per second, e.g., 0.25 Mrad/s, 0.35 Mrad/s, 0.5 Mrad/s, 0.75
Mrad/s or even greater than 1 Mrad/sec, biomass materials can
retain significant quantities of heat so that the temperature of
the biomass materials becomes elevated. While higher temperatures
can, in some embodiments, be advantageous, e.g., when a faster
reaction rate is desired, it is advantageous to control the heating
of the biomass to retain control over the chemical reactions
initiated by the ionizing radiation, such as crosslinking, chain
scission and/or grafting, e.g., to maintain process control. Low
bulk density materials, such as those having a bulk density of less
than about 0.4 g/cm.sup.3, e.g., less than about 0.35, 0.25 or less
about 0.15 g/cm.sup.3, especially when combined with materials that
have thin cross-sections, such as fibers having small transverse
dimensions, are generally easier to cool. In addition, photons and
particles can generally penetrate further into and through
materials having a relatively low bulk density, which can allow for
the processing of larger volumes of materials at higher rates, and
can allow for the use of photons and particles that having lower
energies, e.g., 0.25 Mev, 0.5 MeV, 0.75 MeV or 1.0 MeV, which can
reduce safety shielding requirements. Many of the biomass materials
described herein can be processed in one or more of the systems
shown in FIGS. 11B, 11C, 11D and 11E, which are described below.
The systems shown allow one or more types of ionizing radiation,
such as relativistic electrons or electrons in combination with
X-rays, to be applied to low bulk density biomass materials at high
dose rates, such as at a rate greater than 1.0, 1.5, 2.5 Mrad/s or
even greater than about 5.0 Mrad/s, and then to allow for cooling
of the biomass prior to applying radiation for a second, third,
fourth, fifth, sixth, seventh, eighth, ninth or even a tenth
time.
For example, in one method of changing a molecular and/or a
supramolecular structure of a biomass feedstock, the biomass is
pretreated at a first temperature with ionizing radiation, such as
photons, electrons or ions (e.g., singularly or multiply charged
cations or anions), for a sufficient time and/or a sufficient dose
to elevate the biomass feedstock to a second temperature higher
than the first temperature. The pretreated biomass is then cooled
to a third temperature below the second temperature. Finally, if
desired, the cooled biomass can be treated one or more times with
radiation, e.g., with ionizing radiation. If desired, cooling can
be applied to the biomass after and/or during each radiation
treatment.
The biomass feedstock can be physically prepared as discussed
above, e.g., by reducing one or more dimensions of individual
pieces of the biomass feedstock so that the feedstock can be more
efficiently processed, e.g., more easily cooled and/or more easily
penetrated by an ionizing radiation.
In some implementations, the ionizing radiation is applied at a
total dose of less than 25 Mrad or less than 10 Mrad, such as less
than 5 Mrad or less than 2.5 Mrad, and at a rate of more than 0.25
Mrad per second, such as more than 0.5, 0.75 or greater than 1.0
Mrad/s, prior to cooling the biomass.
The pretreating of the biomass feedstock with ionizing radiation
can be performed as the biomass feedstock is being pneumatically
conveyed in a fluid, such as a in a gas, e.g., nitrogen or air. To
aid in molecular weight breakdown and/or functionalization of the
materials, the gas can be saturated with any swelling agent
described herein and/or water vapor. For example, acidic water
vapor can be utilized. To aid in molecular weight breakdown, the
water can be acidified with an organic acid, such as formic, or
acetic acid, or a mineral acid, such as sulfuric or hydrochloric
acid.
The pretreating of the biomass feedstock with ionizing radiation
can be performed as the biomass feedstock falls under the influence
of gravity. This procedure can effectively reduce the bulk density
of the biomass feedstock as it is being processed and can aid in
the cooling of the biomass feedstock. For example, the biomass can
be conveyed from a first belt at a first height above the ground
and then can be captured by a second belt at a second level above
the ground lower than the first level. For example, in some
embodiments, the trailing edge of the first belt and the leading
edge of the second belt define a gap. Advantageously, the ionizing
radiation, such as a beam of electrons, protons, or other ions, can
be applied at the gap to prevent damage to the biomass conveyance
system.
Cooling of the biomass can include contacting the biomass with a
fluid, such as a gas, at a temperature below the first or second
temperature, such as gaseous nitrogen at or about 77 K. Even water,
such as water at a temperature below nominal room temperature
(e.g., 25 degrees Celsius) can be utilized.
Often advantageously, the biomass feedstock has internal fibers,
and prior to irradiation with the ionizing radiation, the biomass
feedstock has been sheared to an extent that its internal fibers
are substantially exposed. This shearing can provide a low bulk
density material having small cross-sectional dimensions, which can
aid in the breakdown and/or functionalization of the biomass. For
example, in some embodiments, the biomass is or includes discrete
fibers and/or particles having a maximum dimension of not more than
about 0.5 mm, such as not more than about 0.25 mm, not more than
about 0.1 mm or not more than about 0.05 mm.
In some embodiments, the biomass feedstock to which the ionizing
radiation is applied has a bulk density of less than about 0.35
g/cm.sup.3, such as less than about 0.3, 0.25, 0.20, or less than
about 0.15 g/cm.sup.3 during the application of the ionizing
radiation. In such embodiments, the biomass feedstock can be
cooled, and then ionizing radiation can be applied to the cooled
biomass. In some advantageous embodiments, the biomass feedstock is
or includes discrete fibers and/or particles having a maximum
dimension of not more than about 0.5 mm, such as not more than
about 0.25 mm, not more than about 0.1 mm, not more than about 0.05
mm, or not more than about 0.025 mm.
FIGS. 11B and 11C show a fibrous material generating, treating,
conveying and irradiating device 1170 (shielding not illustrated in
the drawings). In operation, paper sheet 1173, e.g., scrap bleached
Kraft paper sheet, is supplied from a roll 1172 and delivered to a
fiberizing apparatus 1174, such as a rotary shearer. The sheet 1173
is converted into fibrous material 1112 and is delivered to a
fiber-loading zone 1180 by conveyer 1178. If desired, the fibers of
the fibrous material can be separated, e.g., by screening, into
fractions having different L/D ratios. In some embodiments, the
fibrous material 1112 of generally a low bulk density and
advantageously thin cross-section, is delivered continuously to
zone 1180; in other embodiments, the fibrous material is delivered
in batches. A blower 1182 in loop 1184 is positioned adjacent to
the fiber-loading zone 1180 and is capable of moving a fluid
medium, e.g., air, at a velocity and volume sufficient to
pneumatically circulate the fibrous material 1112 in a direction
indicated by arrow 1188 through loop 1184.
In some embodiments, the velocity of air traveling in the loop is
sufficient to uniformly disperse and transport the fibrous material
around the entire loop 1184. In some embodiments, the velocity of
flow is greater than 2,500 feet/minute, e.g., 5,000 feet/minute,
6,000 feet/minute or more, e.g., 7,500 feet/minute or 8,500
feet/minute.
The entrained fibrous material 1112 traversing the loop passes an
application zone 1190, which forms part of loop 1184. Here, any
desired additives described herein are applied, such as a liquid,
such as water, which may be acidified or made basic. In operation,
application zone 1190 applies an additive, such as a liquid
solution 1196, to the circulating fibrous material via nozzles 98,
99 and 11100. When a liquid is applied, the nozzles produce an
atomized spray or mist, which impacts the fibers as the fibers pass
in proximity to the nozzles. Valve 11102 is operated to control the
flow of liquid to the respective nozzles 1198, 1199, and 11100.
After a desired quantity of additive is applied, the valve 11102 is
closed.
In some embodiments, the application zone 1190 is two to one
hundred feet long or more, e.g., 125 feet, 150 feet, 250 feet long
or more, e.g., 500 feet long. Longer application zones allow for
application of liquid over a longer period of time during passage
of fibrous material through application zone 1190. In some
embodiments, the nozzles are spaced apart, e.g., by from about
three to about four feet, along the length of loop 1184.
As the fibrous material moves in loop 1184 and through the
irradiating portion of the loop 11107 that includes a horn 11109
for delivering ionizing radiation, ionizing radiation is applied to
the fibrous material (shielding is not shown).
As the irradiated fibrous material moves around loop 1184, it cools
by the action of gases, such as air, circulating at high speeds in
the loop. The material is bathed in reactive gases, such as ozone
and/or oxides of nitrogen, that are produced from the action of the
ionizing radiation on the circulating gases, such as air. After
passing through the irradiating portion 11107, a cooling fluid,
such as a liquid (e.g., water) or a gas, such as liquid nitrogen at
77 K, can be injected into loop 1184 to aid in the cooling of the
fibrous material. This process can be repeated more than one time
if desired, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10 times or more, e.g.,
15 times, to deliver the desired dose to the fibrous material.
While, as shown, the long axis of the horn is along the direction
of flow, in some implementations, the long axis of the horn is
transverse to the direction of the flow. In some implementations, a
beam of electrons is utilized as a principal ionizing radiation
source and X-rays as a secondary ionizing radiation source. X-rays
can be generated by having a metal target, such as a tantalum
target 11111, on the inside of loop 1184 such that when electrons
strike the target, X-rays are emitted.
After a desired dose is delivered to the fibrous material, the
fibrous material can be removed from loop 1184 via a separator
11112, which is selectively connected to loop 1184 by section 11114
and gate valve 11116. When valve 11116 is opened, another valve is
also opened to allow air to enter the loop 1184 to compensate for
air exiting through separator 11112.
FIG. 11D shows a fluidized bed fibrous irradiating device 11121
with shielding. Fibrous material in a fluid, such as a gas, such as
air under pressure, is delivered to a shielded containment vessel
11123 via piping 11125 and into a shielded fluidized bed portion
11127. Counter-current streams 11131 of fluid, such as a gas, and
transverse streams 11133 of fluid, such as a gas, that can be the
same as or different from the fluid delivered counter-currently,
combine to cause turbulence in the bed portion. Ionizing radiation
is applied to the fluidized bed portion as the fibrous material is
conveyed through the bed portion. For example, as shown, three
beams of electrons from three Rhodotron.RTM. machines 11135, 11136
and 11137 can be utilized. Advantageously, each beam can penetrate
into the fluidized bed a different depth and/or each beam can emit
electrons of a different energy, such as 1, 3, and 5 MeV. As the
irradiated fibrous material moves through the system, it cools by
the action of gases, such as air, circulating at high speeds in the
system and it is bathed in reactive gases, such as ozone and/or
oxides of nitrogen, that are produced from the action of the
ionizing radiation on the circulating gases, such as air. If
desired, the process can be repeated a desired number of times
until the fibrous material has received a desired dose. While the
fluidized bed has been illustrated such that its long axis is
horizontal with the ground, in other implementations, the long axis
of the bed is perpendicular to the ground so that the fibrous
material falls under the influence of gravity.
FIG. 11E shows another fibrous material conveying and irradiating
device 11140 without shielding. Fibrous material 11144 is delivered
from a bin 11142 to a first conveyer 11150 at a first level above
the ground and then the material is transferred to a second
conveyer 11152 at a lower height than the first conveyer. The
trailing edge 11160 of the first conveyer and the leading edge
11161 of the second conveyer 11152 define a gap with a spacing S.
For example, the spacing S can be between 4 inches and about 24
inches. Material 11144 has enough momentum to free fall under
gravity and then to be captured by the second conveyer 11152
without falling into the gap. During the free fall, ionizing
radiation is applied to the material. This arrangement can be
advantageous in that the ionizing radiation is less likely to
damage the conveying system because the conveying system is not
directly contacted by the radiation.
After the material passes through the irradiating portion, a
cooling fluid, such as a liquid (e.g., water) or a gas, such as
liquid nitrogen at 77 K, can be applied to the material to aid in
the cooling of the fibrous material. This process can be repeated
more than one time if desired, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10
times or more, e.g., 15 times, to deliver the desired dose to the
fibrous material. While, as shown, the long axis of the horn is
transverse to the direction of the material flow, other beam
arrangements are possible. In some implementations, a beam of
electrons is utilized as a principal ionizing radiation source and
X-rays as a secondary ionizing radiation source. X-rays can be
generated by having a metal target, such as a tantalum target, in
the gap on the opposite side of the material, such that as the
electrons that pass through the material they strike the target,
generating X-rays.
Sonication and other Biomass Disruption Processes
One or more sonication processing sequences can be used to process
raw feedstock from a wide variety of different sources to extract
useful substances from the feedstock, and to provide partially
degraded organic material which functions as input to further
processing steps and/or sequences. Sonication can reduce the
molecular weight and/or crystallinity of feedstock, such as one or
more of any of the biomass materials described herein, e.g., one or
more carbohydrate sources, such as cellulosic or lignocellulosic
materials, or starchy materials.
Referring again to FIG. 8, in one method, a first material 2 that
includes cellulose having a first number average molecular weight
(.sup.TM.sub.N1) is dispersed in a medium, such as water, and
sonicated and/or otherwise cavitated, to provide a second material
3 that includes cellulose having a second number average molecular
weight (.sup.TM.sub.N2) lower than the first number average
molecular weight. The second material (or the first and second
material in certain embodiments) can be combined with a
microorganism (e.g., a bacterium or a yeast) that can utilize the
second and/or first material to produce a fuel 5 that is or
includes hydrogen, an alcohol, an organic acid, a hydrocarbon or
mixtures of any of these.
Since the second material has cellulose having a reduced molecular
weight relative to the first material, and in some instances, a
reduced crystallinity as well, the second material is generally
more dispersible, swellable, and/or soluble in a solution
containing the microorganism, e.g., at a concentration of greater
than 10.sup.6 microorganisms/mL. These properties make the second
material 3 more susceptible to chemical, enzymatic, and/or
microbial attack relative to the first material 2, which can
greatly improve the production rate and/or production level of a
desired product, e.g., ethanol. Sonication can also sterilize the
materials, but should not be used while the microorganisms are
supposed to be alive.
In some embodiments, the second number average molecular weight
(.sup.TM.sub.N2) is lower than the first number average molecular
weight (.sup.TM.sub.N1) by more than about 10 percent, e.g., 15,
20, 25, 30, 35, 40, 50 percent, 60 percent, or even more than about
75 percent.
In some instances, the second material has cellulose that has as
crystallinity (.sup.TC.sub.2) that is lower than the crystallinity
(.sup.TC.sub.1) of the cellulose of the first material. For
example, (.sup.TC.sub.2) can be lower than (.sup.TC.sub.1) by more
than about 10 percent, e.g., 15, 20, 25, 30, 35, 40, or even more
than about 50 percent.
In some embodiments, the starting crystallinity index (prior to
sonication) is from about 40 to about 87.5 percent, e.g., from
about 50 to about 75 percent or from about 60 to about 70 percent,
and the crystallinity index after sonication is from about 10 to
about 50 percent, e.g., from about 15 to about 45 percent or from
about 20 to about 40 percent. However, in certain embodiments,
e.g., after extensive sonication, it is possible to have a
crystallinity index of lower than 5 percent. In some embodiments,
the material after sonication is substantially amorphous.
In some embodiments, the starting number average molecular weight
(prior to sonication) is from about 200,000 to about 3,200,000,
e.g., from about 250,000 to about 1,000,000 or from about 250,000
to about 700,000, and the number average molecular weight after
sonication is from about 50,000 to about 200,000, e.g., from about
60,000 to about 150,000 or from about 70,000 to about 125,000.
However, in some embodiments, e.g., after extensive sonication, it
is possible to have a number average molecular weight of less than
about 10,000 or even less than about 5,000.
In some embodiments, the second material can have a level of
oxidation (.sup.TO.sub.2) that is higher than the level of
oxidation (.sup.TO.sub.1) of the first material. A higher level of
oxidation of the material can aid in its dispersibility,
swellability and/or solubility, further enhancing the materials
susceptibility to chemical, enzymatic or microbial attack. In some
embodiments, to increase the level of the oxidation of the second
material relative to the first material, the sonication is
performed in an oxidizing medium, producing a second material that
is more oxidized than the first material. For example, the second
material can have more hydroxyl groups, aldehyde groups, ketone
groups, ester groups or carboxylic acid groups, which can increase
its hydrophilicity.
In some embodiments, the sonication medium is an aqueous medium. If
desired, the medium can include an oxidant, such as a peroxide
(e.g., hydrogen peroxide), a dispersing agent and/or a buffer.
Examples of dispersing agents include ionic dispersing agents,
e.g., sodium lauryl sulfate, and non-ionic dispersing agents, e.g.,
poly(ethylene glycol).
In other embodiments, the sonication medium is non-aqueous. For
example, the sonication can be performed in a hydrocarbon, e.g.,
toluene or heptane, an ether, e.g., diethyl ether or
tetrahydrofuran, or even in a liquefied gas such as argon, xenon,
or nitrogen.
Without wishing to be bound by any particular theory, it is
believed that sonication breaks bonds in the cellulose by creating
bubbles in the medium containing the cellulose, which grow and then
violently collapse. During the collapse of the bubble, which can
take place in less than a nanosecond, the implosive force raises
the local temperature within the bubble to about 5100 K (even
higher in some instance; see, e.g., Suslick et al., Nature 434,
52-55) and generates pressures of from a few hundred atmospheres to
over 1000 atmospheres or more. It is these high temperatures and
pressures that break the bonds. In addition, without wishing to be
bound by any particular theory, it is believed that reduced
crystallinity arises, at least in part, from the extremely high
cooling rates during collapse of the bubbles, which can be greater
than about 10.sup.11 K/second. The high cooling rates generally do
not allow the cellulose to organize and crystallize, resulting in
materials that have reduced crystallinity. Ultrasonic systems and
sonochemistry are discussed in, e.g., Olli et al., U.S. Pat. No.
5,766,764; Roberts, U.S. Pat. No. 5,828,156; Mason, Chemistry with
Ultrasound, Elsevier, Oxford, (1990); Suslick (editor), Ultrasound:
its Chemical, Physical and Biological Effects, VCH, Weinheim,
(1988); Price, "Current Trends in Sonochemistry" Royal Society of
Chemistry, Cambridge, (1992); Suslick et al., Ann. Rev. Mater. Sci.
29, 295, (1999); Suslick et al., Nature 353, 414 (1991); Hiller et
al., Phys. Rev. Lett. 69, 1182 (1992); Barber et al., Nature, 352,
414 (1991); Suslick et al., J. Am. Chem. Soc., 108, 5641 (1986);
Tang et al., Chem. Comm., 2119 (2000); Wang et al., Advanced
Mater., 12, 1137 (2000); Landau et al., J. of Catalysis, 201, 22
(2001); Perkas et al., Chem. Comm., 988 (2001); Nikitenko et al.,
Angew. Chem. Inter. Ed. (December 2001); Shafi et al., J. Phys.
Chem. B 103, 3358 (1999); Avivi et al., J. Amer. Chem. Soc. 121,
4196 (1999); and Avivi et al., J. Amer. Chem. Soc. 122, 4331
(2000).
Sonication Systems
FIG. 12 shows a general system in which a cellulosic material
stream 1210 is mixed with a water stream 1212 in a reservoir 1214
to form a process stream 1216. A first pump 1218 draws process
stream 1216 from reservoir 1214 and toward a flow cell 1224.
Ultrasonic transducer 1226 transmits ultrasonic energy into process
stream 1216 as the process stream flows through flow cell 1224. A
second pump 1230 draws process stream 1216 from flow cell 1224 and
toward subsequent processing.
Reservoir 1214 includes a first intake 1232 and a second intake
1234 in fluid communication with a volume 1236. A conveyor (not
shown) delivers cellulosic material stream 1210 to reservoir 1214
through first intake 1232. Water stream 1212 enters reservoir 1214
through second intake 1234. In some embodiments, water stream 1212
enters volume 1236 along a tangent establishing a swirling flow
within volume 1236. In certain embodiments, cellulosic material
stream 1210 and water stream 1212 can be introduced into volume
1236 along opposing axes to enhance mixing within the volume.
Valve 1238 controls the flow of water stream 1212 through second
intake 1232 to produce a desired ratio of cellulosic material to
water (e.g., approximately 10% cellulosic material, weight by
volume). For example, 2000 tons/day of cellulosic material can be
combined with 1 million to 1.5 million gallons/day, e.g., 1.25
million gallons/day, of water.
Mixing of cellulosic material and water in reservoir 1214 is
controlled by the size of volume 1236 and the flow rates of
cellulosic material and water into the volume. In some embodiments,
volume 1236 is sized to create a minimum mixing residence time for
the cellulosic material and water. For example, when 2000 tons/day
of cellulosic material and 1.25 million gallons/day of water are
flowing through reservoir 1214, volume 1236 can be about 32,000
gallons to produce a minimum mixing residence time of about 15
minutes.
Reservoir 1214 includes a mixer 1240 in fluid communication with
volume 1236. Mixer 1240 agitates the contents of volume 1236 to
disperse cellulosic material throughout the water in the volume.
For example, mixer 1240 can be a rotating vane disposed in
reservoir 1214. In some embodiments, mixer 1240 disperses the
cellulosic material substantially uniformly throughout the
water.
Reservoir 1214 further includes an exit 1242 in fluid communication
with volume 1236 and process stream 1216. The mixture of cellulosic
material and water in volume 1236 flows out of reservoir 1214 via
exit 1242. Exit 1242 is arranged near the bottom of reservoir 1214
to allow gravity to pull the mixture of cellulosic material and
water out of reservoir 1214 and into process stream 1216.
First pump 1218 (e.g., any of several recessed impeller vortex
pumps made by Essco Pumps & Controls, Los Angeles, Calif.)
moves the contents of process stream 1216 toward flow cell 1224. In
some embodiments, first pump 1218 agitates the contents of process
stream 1216 such that the mixture of cellulosic material and water
is substantially uniform at inlet 1220 of flow cell 1224. For
example, first pump 1218 agitates process stream 1216 to create a
turbulent flow that persists along the process stream between the
first pump and inlet 1220 of flow cell 1224.
Flow cell 1224 includes a reactor volume 1244 in fluid
communication with inlet 1220 and outlet 1222. In some embodiments,
reactor volume 1244 is a stainless steel tube capable of
withstanding elevated pressures (e.g., 10 bars). In addition or in
the alternative, reactor volume 1244 includes a rectangular cross
section.
Flow cell 1224 further includes a heat exchanger 1246 in thermal
communication with at least a portion of reactor volume 1244.
Cooling fluid 1248 (e.g., water) flows into heat exchanger 1246 and
absorbs heat generated when process stream 1216 is sonicated in
reactor volume 1244. In some embodiments, the flow rate and/or the
temperature of cooling fluid 1248 into heat exchanger 1246 is
controlled to maintain an approximately constant temperature in
reactor volume 1244. In some embodiments, the temperature of
reactor volume 1244 is maintained at 20 to 50.degree. C., e.g., 25,
30, 35, 40, or 45.degree. C. Additionally or alternatively, heat
transferred to cooling fluid 1248 from reactor volume 1244 can be
used in other parts of the overall process.
An adapter section 1226 creates fluid communication between reactor
volume 1244 and a booster 1250 coupled (e.g., mechanically coupled
using a flange) to ultrasonic transducer 1226. For example, adapter
section 1226 can include a flange and O-ring assembly arranged to
create a leak tight connection between reactor volume 1244 and
booster 1250. In some embodiments, ultrasonic transducer 1226 is a
high-powered ultrasonic transducer made by Hielscher Ultrasonics of
Teltow, Germany.
In operation, a generator 1252 delivers electricity to ultrasonic
transducer 1252. Ultrasonic transducer 1226 includes a
piezoelectric element that converts the electrical energy into
sound in the ultrasonic range. In some embodiments, the materials
are sonicated using sound having a frequency of from about 16 kHz
to about 110 kHz, e.g., from about 18 kHz to about 75 kHz or from
about 20 kHz to about 40 kHz. (e.g., sound having a frequency of 20
kHz to 40 kHz). In some implementations, sonication is performed,
for example, at a frequency of between about 15 kHz and about 25
kHz, such as between about 18 kHz and 22 kHz. In specific
embodiments, sonicating can performed utilizing a 1 KW or larger
horn, e.g., a 2, 3, 4, 5, or even a 10 KW horn.
The ultrasonic energy is then delivered to the working medium
through booster 1248. The ultrasonic energy traveling through
booster 1248 in reactor volume 1244 creates a series of
compressions and rarefactions in process stream 1216 with an
intensity sufficient to create cavitation in process stream 1216.
Cavitation disaggregates the cellulosic material dispersed in
process stream 1216. Cavitation also produces free radicals in the
water of process stream 1216. These free radicals act to further
break down the cellulosic material in process stream 1216.
In general, 5 to 4000 MJ/m.sup.3, e.g., 10, 25, 50, 100, 250, 500,
750, 1000, 2000, or 3000 MJ/m.sup.3, of ultrasonic energy is
applied to process stream 16 flowing at a rate of about 0.2
m.sup.3/s (about 3200 gallons/min). After exposure to ultrasonic
energy in reactor volume 1244, process stream 1216 exits flow cell
1224 through outlet 1222. Second pump 1230 moves process stream
1216 to subsequent processing (e.g., any of several recessed
impeller vortex pumps made by Essco Pumps & Controls, Los
Angeles, Calif.).
While certain embodiments have been described, other embodiments
are possible.
As an example, while process stream 1216 has been described as a
single flow path, other arrangements are possible. In some
embodiments for example, process stream 1216 includes multiple
parallel flow paths (e.g., flowing at a rate of 10 gallon/min). In
addition or in the alternative, the multiple parallel flow paths of
process stream 1216 flow into separate flow cells and are sonicated
in parallel (e.g., using a plurality of 16 kW ultrasonic
transducers).
As another example, while a single ultrasonic transducer 1226 has
been described as being coupled to flow cell 1224, other
arrangements are possible. In some embodiments, a plurality of
ultrasonic transducers 1226 are arranged in flow cell 1224 (e.g.,
ten ultrasonic transducers can be arranged in a flow cell 1224). In
some embodiments, the sound waves generated by each of the
plurality of ultrasonic transducers 1226 are timed (e.g.,
synchronized out of phase with one another) to enhance the
cavitation acting upon process stream 1216.
As another example, while a single flow cell 1224 has been
described, other arrangements are possible. In some embodiments,
second pump 1230 moves process stream to a second flow cell where a
second booster and ultrasonic transducer further sonicate process
stream 1216.
As still another example, while reactor volume 1244 has been
described as a closed volume, reactor volume 1244 is open to
ambient conditions in certain embodiments. In such embodiments,
sonication pretreatment can be performed substantially
simultaneously with other pretreatment techniques. For example,
ultrasonic energy can be applied to process stream 1216 in reactor
volume 1244 while electron beams are simultaneously introduced into
process stream 1216.
As another example, while a flow-through process has been
described, other arrangements are possible. In some embodiments,
sonication can be performed in a batch process. For example, a
volume can be filled with a 10% (weight by volume) mixture of
cellulosic material in water and exposed to sound with intensity
from about 50 W/cm.sup.2 to about 600 W/cm.sup.2, e.g., from about
75 W/cm.sup.2 to about 300 W/cm.sup.2 or from about 95 W/cm.sup.2
to about 200 W/cm.sup.2. Additionally or alternatively, the mixture
in the volume can be sonicated from about 1 hour to about 24 hours,
e.g., from about 1.5 hours to about 12 hours, or from about 2 hours
to about 10 hours. In certain embodiments, the material is
sonicated for a pre-determined time, and then allowed to stand for
a second pre-determined time before sonicating again.
Referring now to FIG. 13, in some embodiments, two electroacoustic
transducers are mechanically coupled to a single horn. As shown, a
pair of piezoelectric transducers 60 and 62 is coupled to a slotted
bar horn 64 by respective intermediate coupling horns 70 and 72,
the latter also being known as booster horns. The mechanical
vibrations provided by the transducers, responsive to high
frequency electrical energy applied thereto, are transmitted to the
respective coupling horns, which may be constructed to provide a
mechanical gain, such as a ratio of 1 to 1.2. The horns are
provided with a respective mounting flange 74 and 76 for supporting
the transducer and horn assembly in a stationary housing.
The vibrations transmitted from the transducers through the
coupling or booster horns are coupled to the input surface 78 of
the horn and are transmitted through the horn to the oppositely
disposed output surface 80, which, during operation, is in forced
engagement with a workpiece (not shown) to which the vibrations are
applied.
The high frequency electrical energy provided by the power supply
82 is fed to each of the transducers, electrically connected in
parallel, via a balancing transformer 84 and a respective series
connected capacitor 86 and 90, one capacitor connected in series
with the electrical connection to each of the transducers. The
balancing transformer is known also as "balun" standing for
"balancing unit." The balancing transformer includes a magnetic
core 92 and a pair of identical windings 94 and 96, also termed the
primary winding and secondary winding, respectively.
In some embodiments, the transducers include commercially available
piezoelectric transducers, such as Branson Ultrasonics Corporation
models 105 or 502, each designed for operation at 20 kHz and a
maximum power rating of 3 kW. The energizing voltage for providing
maximum motional excursion at the output surface of the transducer
is 930 volt rms. The current flow through a transducer may vary
between zero and 3.5 ampere depending on the load impedance. At 930
volt rms the output motion is approximately 20 microns. The maximum
difference in terminal voltage for the same motional amplitude,
therefore, can be 186 volt. Such a voltage difference can give rise
to large circulating currents flowing between the transducers. The
balancing unit 430 assures a balanced condition by providing equal
current flow through the transducers, hence eliminating the
possibility of circulating currents. The wire size of the windings
must be selected for the full load current noted above and the
maximum voltage appearing across a winding input is 93 volt.
While ultrasonic transducer 1226 has been described as including
one or more piezoelectric active elements to create ultrasonic
energy, other arrangements are possible. In some embodiments,
ultrasonic transducer 1226 includes active elements made of other
types of magnetostrictive materials (e.g., ferrous metals). Design
and operation of such a high-powered ultrasonic transducer is
discussed in Hansen et al., U.S. Pat. No. 6,624,539. In some
embodiments, ultrasonic energy is transferred to process stream 16
through an electrohydraulic system.
While ultrasonic transducer 1226 has been described as using the
electromagnetic response of magnetorestrictive materials to produce
ultrasonic energy, other arrangements are possible. In some
embodiments, acoustic energy in the form of an intense shock wave
can be applied directly to process stream 16 using an underwater
spark. In some embodiments, ultrasonic energy is transferred to
process stream 16 through a thermohydraulic system. For example,
acoustic waves of high energy density can be produced by applying
power across an enclosed volume of electrolyte, thereby heating the
enclosed volume and producing a pressure rise that is subsequently
transmitted through a sound propagation medium (e.g., process
stream 1216). Design and operation of such a thermohydraulic
transducer is discussed in Hartmann et al., U.S. Pat. No.
6,383,152.
Some embodiments use a high frequency, rotor-stator device. This
type of device produces high-shear, microcavitation forces, which
can disintegrate biomass in contact with such forces. Two
commercially available high-frequency, rotor-stator dispersion
devices are the Supraton.TM. devices manufactured by Krupp
Industrietechnik GmbH and marketed by Dorr-Oliver Deutschland GmbH
of Connecticut, and the Dispax.TM. devices manufactured and
marketed by Ika-Works, Inc. of Cincinnati, Ohio. Operation of such
a microcavitation device is discussed in Stuart, U.S. Pat. No.
5,370,999.
In another biomass disruption technique, microwave or radiowave
energy is applied to a treated or untreated biomass material, such
as a lignocellulosic material, in a manner that water within the
biomass material is vaporized, but overall the biomass material
undergoes little bulk heating. For example, a frequency of from
about 10 MHz to about 300,000 MHz can be applied to the biomass
material. In some instances the microwave or radiowave energy is
applied in short pulses, e.g., having a duration of less than 0.1
seconds, e.g., less than 0.05 seconds, less than 0.03 seconds, less
than 0.01 seconds or even less, e.g., 0.005 seconds. Without
wishing to be bound by any particular theory, it is believed when
the microwave or radiowave energy is applied in this manner, water
is vaporized within the biomass material with explosive force,
which disrupts the lignin and "peels" it away from the cellulose.
At the same time, since application of such energy does not heat
the bulk material, the lignin does not tend to re-apply onto the
cellulose, which could block access to the cellulose, e.g., by an
enzyme or microbe. Many of the properties of lignin are described
Carter Fox in a thesis entitled "Chemical and Thermal
Characterization of Three Industrial Lignin and Their Corresponding
Esters (May 2006, University of Idaho).
In another biomass disruption technique, treated (e.g., using any
treatment method described herein) or untreated biomass material is
subjected to a hot, compressed fluid, such as water. In such a
method, the biomass is placed in a pressure vessel containing a
fluid, such as water, at an elevated temperature, e.g., above 50,
60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, or above
180.degree. C. The pressure vessel is placed under gas pressure,
such as under argon, nitrogen or air, and then stirred, e.g., with
a two blade turbine propeller for a period of time, e.g., 10
minutes, 20 minutes, 30 minutes, 45 minutes, 60 minutes or 90
minutes. In some embodiments, the pressure is between about 500
psig and 2000 psig, e.g., between about 650 psig and about 1500
psig or between about 700 psig and about 1200 psig. In some
embodiments, the temperature is at or 5 or 10.degree. C. above a
glass transition temperature for the lignin. Without wishing to be
bound by any particular theory, it is believed that when the
temperature is above the glass transition temperature of the
lignin, the conditions in the pressure vessel cause the lignin to
"peel" away from the cellulose, making the cellulose more exposed
for breakdown, e.g., by an enzyme.
In another biomass disruption technique, treated, e.g., irradiated,
or untreated biomass material is delivered to a nip defined between
two counter rotating pressure rolls, which can be optionally
heated. Pressure in the nip can be adjusted by the amount of
biomass material fed into the nip and the spacing between the
pressure rolls. In some embodiments, the pressure in the nip can be
greater than 1,000 psi per linear inch, e.g., greater than 2,500
psi, greater than 5,000 psi, greater than 7,500 psi, greater than
10,000 psi, or even greater than 15,000 psi per linear inch. In
some embodiments, the pressure rolls are operated at an elevated
temperature, e.g., above 50, 60, 70, 80, 90, 100, 110, 120, 130,
140, 150, 160, 170, or above 180.degree. C. In some embodiments,
the rolls are operated at a temperature above a glass transition
temperature of the lignin. Without wishing to be bound by any
particular theory, it is believed that the pressure and heat in the
nip can disrupt any lignin of the biomass material, making the
cellulose more accessible and available to an enzyme.
Pyrolysis
One or more pyrolysis processing sequences can be used to process
raw feedstock from a wide variety of different sources to extract
useful substances from the feedstock, and to provide partially
degraded organic material which functions as input to further
processing steps and/or sequences.
Referring again to the general schematic in FIG. 8, a first
material 2 that includes cellulose having a first number average
molecular weight (.sup.TM.sub.N1) is pyrolyzed, e.g., by heating
the first material in a tube furnace, to provide a second material
3 that includes cellulose having a second number average molecular
weight (.sup.TM.sub.N2) lower than the first number average
molecular weight. The second material (or the first and second
material in certain embodiments) is/are combined with a
microorganism (e.g., a bacterium or a yeast) that can utilize the
second and/or first material to produce a fuel 5 that is or
includes hydrogen, an alcohol (e.g., ethanol or butanol, such as
n-, sec or t-butanol), an organic acid, a hydrocarbon or mixtures
of any of these.
Since the second material has cellulose having a reduced molecular
weight relative to the first material, and in some instances, a
reduced crystallinity as well, the second material is generally
more dispersible, swellable and/or soluble in a solution containing
the microorganism, e.g., at a concentration of greater than
10.sup.6 microorganisms/mL. These properties make the second
material 3 more susceptible to chemical, enzymatic and/or microbial
attack relative to the first material 2, which can greatly improve
the production rate and/or production level of a desired product,
e.g., ethanol. Pyrolysis can also sterilize the first and second
materials.
In some embodiments, the second number average molecular weight
(.sup.TM.sub.N2) is lower than the first number average molecular
weight (.sup.TM.sub.N1) by more than about 10 percent, e.g., 15,
20, 25, 30, 35, 40, 50 percent, 60 percent, or even more than about
75 percent.
In some instances, the second material has cellulose that has as
crystallinity (.sup.TC.sub.2) that is lower than the crystallinity
(.sup.TC.sub.1) of the cellulose of the first material. For
example, (.sup.TC.sub.2) can be lower than (.sup.TC.sub.1) by more
than about 10 percent, e.g., 15, 20, 25, 30, 35, 40, or even more
than about 50 percent.
In some embodiments, the starting crystallinity (prior to
pyrolysis) is from about 40 to about 87.5 percent, e.g., from about
50 to about 75 percent or from about 60 to about 70 percent, and
the crystallinity index after pyrolysis is from about 10 to about
50 percent, e.g., from about 15 to about 45 percent or from about
20 to about 40 percent. However, in certain embodiments, e.g.,
after extensive pyrolysis, it is possible to have a crystallinity
index of lower than 5 percent. In some embodiments, the material
after pyrolysis is substantially amorphous.
In some embodiments, the starting number average molecular weight
(prior to pyrolysis) is from about 200,000 to about 3,200,000,
e.g., from about 250,000 to about 1,000,000 or from about 250,000
to about 700,000, and the number average molecular weight after
pyrolysis is from about 50,000 to about 200,000, e.g., from about
60,000 to about 150,000 or from about 70,000 to about 125,000.
However, in some embodiments, e.g., after extensive pyrolysis, it
is possible to have a number average molecular weight of less than
about 10,000 or even less than about 5,000.
In some embodiments, the second material can have a level of
oxidation (.sup.TO.sub.2) that is higher than the level of
oxidation (.sup.TO.sub.1) of the first material. A higher level of
oxidation of the material can aid in its dispersibility,
swellability and/or solubility, further enhancing the materials
susceptibility to chemical, enzymatic or microbial attack. In some
embodiments, to increase the level of the oxidation of the second
material relative to the first material, the pyrolysis is performed
in an oxidizing environment, producing a second material that is
more oxidized than the first material. For example, the second
material can have more hydroxyl groups, aldehyde groups, ketone
groups, ester groups or carboxylic acid groups, which can increase
its hydrophilicity.
In some embodiments, the pyrolysis of the materials is continuous.
In other embodiments, the material is pyrolyzed for a
pre-determined time, and then allowed to cool for a second
pre-determined time before pyrolyzing again.
Pyrolysis Systems
FIG. 14 shows a process flow diagram 6000 that includes various
steps in a pyrolytic feedstock pretreatment system. In first step
6010, a supply of dry feedstock is received from a feed source.
As described above, the dry feedstock from the feed source may be
pre-processed prior to delivery to the pyrolysis chamber. For
example, if the feedstock is derived from plant sources, certain
portions of the plant material may be removed prior to collection
of the plant material and/or before the plant material is delivered
by the feedstock transport device. Alternatively, or in addition,
the biomass feedstock can be subjected to mechanical processing
6020 (e.g., to reduce the average length of fibers in the
feedstock) prior to delivery to the pyrolysis chamber.
Following mechanical processing, the feedstock undergoes a moisture
adjustment step 6030. The nature of the moisture adjustment step
depends upon the moisture content of the mechanically processed
feedstock. Typically, pyrolysis of feedstock occurs most
efficiently when the moisture content of the feedstock is between
about 10% and about 30% (e.g., between 15% and 25%) by weight of
the feedstock. If the moisture content of the feedstock is larger
than about 40% by weight, the extra thermal load presented by the
water content of the feedstock increases the energy consumption of
subsequent pyrolysis steps.
In some embodiments, if the feedstock has a moisture content which
is larger than about 30% by weight, drier feedstock material 6220,
which has a low moisture content, can be blended in, creating a
feedstock mixture in step 6030 with an average moisture content
that is within the limits discussed above. In certain embodiments,
feedstock with a high moisture content can simply be dried by
dispersing the feedstock material on a moving conveyor that cycles
the feedstock through an in-line heating unit. The heating unit
evaporates a portion of the water present in the feedstock.
In some embodiments, if the feedstock from step 6020 has a moisture
content which is too low (e.g., lower than about 10% by weight),
the mechanically processed feedstock can be combined with wetter
feedstock material 6230 with a higher moisture content, such as
sewage sludge. Alternatively, or in addition, water 6240 can be
added to the dry feedstock from step 6020 to increase its moisture
content.
In step 6040, the feedstock--now with its moisture content adjusted
to fall within suitable limits--can be preheated in an optional
preheating step 6040. Preheating step 6040 can be used to increase
the temperature of the feedstock to between 75.degree. C. and
150.degree. C. in preparation for subsequent pyrolysis of the
feedstock. Depending upon the nature of the feedstock and the
particular design of the pyrolysis chamber, preheating the
feedstock can ensure that heat distribution within the feedstock
remains more uniform during pyrolysis, and can reduce the thermal
load on the pyrolysis chamber.
The feedstock is then transported to a pyrolysis chamber to undergo
pyrolysis in step 6050. In some embodiments, transport of the
feedstock is assisted by adding one or more pressurized gases 6210
to the feedstock stream. The gases create a pressure gradient in a
feedstock transport conduit, propelling the feedstock into the
pyrolysis chamber (and even through the pyrolysis chamber). In
certain embodiments, transport of the feedstock occurs
mechanically; that is, a transport system that includes a conveyor
such as an auger transports the feedstock to the pyrolysis
chamber.
Other gases 6210 can also be added to the feedstock prior to the
pyrolysis chamber. In some embodiments, for example, one or more
catalyst gases can be added to the feedstock to assist
decomposition of the feedstock during pyrolysis. In certain
embodiments, one or more scavenging agents can be added to the
feedstock to trap volatile materials released during pyrolysis. For
example, various sulfur-based compounds such as sulfides can be
liberated during pyrolysis, and an agent such as hydrogen gas can
be added to the feedstock to cause desulfurization of the pyrolysis
products. Hydrogen combines with sulfides to form hydrogen sulfide
gas, which can be removed from the pyrolyzed feedstock.
Pyrolysis of the feedstock within the chamber can include heating
the feedstock to relatively high temperatures to cause partial
decomposition of the feedstock. Typically, the feedstock is heated
to a temperature in a range from 150.degree. C. to 1100.degree. C.
The temperature to which the feedstock is heated depends upon a
number of factors, including the composition of the feedstock, the
feedstock average particle size, the moisture content, and the
desired pyrolysis products. For many types of biomass feedstock,
for example, pyrolysis temperatures between 300.degree. C. and
550.degree. C. are used.
The residence time of the feedstock within the pyrolysis chamber
generally depends upon a number of factors, including the pyrolysis
temperature, the composition of the feedstock, the feedstock
average particle size, the moisture content, and the desired
pyrolysis products. In some embodiments, feedstock materials are
pyrolyzed at a temperature just above the decomposition temperature
for the material in an inert atmosphere, e.g., from about 2.degree.
C. above to about 10.degree. C. above the decomposition temperature
or from about 3.degree. C. above to about 7.degree. C. above the
decomposition temperature. In such embodiments, the material is
generally kept at this temperature for greater than 0.5 hours,
e.g., greater than 1.0 hour or greater than about 2.0 hours. In
other embodiments, the materials are pyrolyzed at a temperature
well above the decomposition temperature for the material in an
inert atmosphere, e.g., from about 75.degree. C. above to about
175.degree. C. above the decomposition temperature or from about
85.degree. C. above to about 150.degree. C. above the decomposition
temperature. In such embodiments, the material is generally kept at
this temperature for less than 0.5 hour, e.g., less 20 minutes,
less than 10 minutes, less than 5 minutes or less than 2 minutes.
In still other embodiments, the materials are pyrolyzed at an
extreme temperature, e.g., from about 200.degree. C. above to about
500.degree. C. above the decomposition temperature of the material
in an inert environment or from about 250.degree. C. above to about
400.degree. C. above the decomposition temperature. In such
embodiments, the material us generally kept at this temperature for
less than 1 minute, e.g., less than 30 seconds, 15 seconds, 10
seconds, 5 seconds, 1 second or less than 500 ms. Such embodiments
are typically referred to as flash pyrolysis.
In some embodiments, the feedstock is heated relatively rapidly to
the selected pyrolysis temperature within the chamber. For example,
the chamber can be designed to heat the feedstock at a rate of
between 500.degree. C./s and 11,000.degree. C./s, for example from
500.degree. C./s to 1000.degree. C./s.
A turbulent flow of feedstock material within the pyrolysis chamber
is usually advantageous, as it ensures relatively efficient heat
transfer to the feedstock material from the heating sub-system.
Turbulent flow can be achieved, for example, by blowing the
feedstock material through the chamber using one or more injected
carrier gases 6210. In general, the carrier gases are relatively
inert towards the feedstock material, even at the high temperatures
in the pyrolysis chamber. Exemplary carrier gases include, for
example, nitrogen, argon, methane, carbon monoxide, and carbon
dioxide. Alternatively, or in addition, mechanical transport
systems such as augers can transport and circulate the feedstock
within the pyrolysis chamber to create a turbulent feedstock
flow.
In some embodiments, pyrolysis of the feedstock occurs
substantially in the absence of oxygen and other reactive gases.
Oxygen can be removed from the pyrolysis chamber by periodic
purging of the chamber with high pressure nitrogen (e.g., at
nitrogen pressures of 2 bar or more). Following purging of the
chamber, a gas mixture present in the pyrolysis chamber (e.g.,
during pyrolysis of the feedstock) can include less than 4 mole %
oxygen (e.g., less than 1 mole % oxygen, and even less than 0.5
mole % oxygen). The absence of oxygen ensures that ignition of the
feedstock does not occur at the elevated pyrolysis
temperatures.
In certain embodiments, relatively small amounts of oxygen can be
introduced into the feedstock and are present during pyrolysis.
This technique is referred to as oxidative pyrolysis. Typically,
oxidative pyrolysis occurs in multiple heating stages. For example,
in a first heating stage, the feedstock is heated in the presence
of oxygen to cause partial oxidation of the feedstock. This stage
consumes the available oxygen in the pyrolysis chamber. Then, in
subsequent heating stages, the feedstock temperature is further
elevated. With all of the oxygen in the chamber consumed, however,
feedstock combustion does not occur, and combustion-free pyrolytic
decomposition of the feedstock (e.g., to generate hydrocarbon
products) occurs. In general, the process of heating feedstock in
the pyrolysis chamber to initiate decomposition is endothermic.
However, in oxidative pyrolysis, formation of carbon dioxide by
oxidation of the feedstock is an exothermic process. The heat
released from carbon dioxide formation can assist further pyrolysis
heating stages, thereby lessening the thermal load presented by the
feedstock.
In some embodiments, pyrolysis occurs in an inert environment, such
as while feedstock materials are bathed in argon or nitrogen gas.
In certain embodiments, pyrolysis can occur in an oxidizing
environment, such as in air or argon enriched in air. In some
embodiments, pyrolysis can take place in a reducing environment,
such as while feedstock materials are bathed in hydrogen gas. To
aid pyrolysis, various chemical agents, such as oxidants,
reductants, acids or bases can be added to the material prior to or
during pyrolysis. For example, sulfuric acid can be added, or a
peroxide (e.g., benzoyl peroxide) can be added.
As discussed above, a variety of different processing conditions
can be used, depending upon factors such as the feedstock
composition and the desired pyrolysis products. For example, for
cellulose-containing feedstock material, relatively mild pyrolysis
conditions can be employed, including flash pyrolysis temperatures
between 375.degree. C. and 450.degree. C., and residence times of
less than 1 second. As another example, for organic solid waste
material such as sewage sludge, flash pyrolysis temperatures
between 500.degree. C. and 650.degree. C. are typically used, with
residence times of between 0.5 and 3 seconds. In general, many of
the pyrolysis process parameters, including residence time,
pyrolysis temperature, feedstock turbulence, moisture content,
feedstock composition, pyrolysis product composition, and additive
gas composition can be regulated automatically by a system of
regulators and an automated control system.
Following pyrolysis step 6050, the pyrolysis products undergo a
quenching step 6250 to reduce the temperature of the products prior
to further processing. Typically, quenching step 6250 includes
spraying the pyrolysis products with streams of cooling water 6260.
The cooling water also forms a slurry that includes solid,
undissolved product material and various dissolved products. Also
present in the product stream is a mixture that includes various
gases, including product gases, carrier gases, and other types of
process gases.
The product stream is transported via in-line piping to a gas
separator that performs a gas separation step 6060, in which
product gases and other gases are separated from the slurry formed
by quenching the pyrolysis products. The separated gas mixture is
optionally directed to a blower 6130, which increases the gas
pressure by blowing air into the mixture. The gas mixture can be
subjected to a filtration step 6140, in which the gas mixture
passes through one or more filters (e.g., activated charcoal
filters) to remove particulates and other impurities. In a
subsequent step 6150, the filtered gas can be compressed and stored
for further use. Alternatively, the filtered gas can be subjected
to further processing steps 6160. For example, in some embodiments,
the filtered gas can be condensed to separate different gaseous
compounds within the gas mixture. The different compounds can
include, for example, various hydrocarbon products (e.g., alcohols,
alkanes, alkenes, alkynes, ethers) produced during pyrolysis. In
certain embodiments, the filtered gas containing a mixture of
hydrocarbon components can be combined with steam gas 6170 (e.g., a
mixture of water vapor and oxygen) and subjected to a cracking
process to reduce molecular weights of the hydrocarbon
components.
In some embodiments, the pyrolysis chamber includes heat sources
that burn hydrocarbon gases such as methane, propane, and/or butane
to heat the feedstock. A portion 6270 of the separated gases can be
recirculated into the pyrolysis chamber for combustion, to generate
process heat to sustain the pyrolysis process.
In certain embodiments, the pyrolysis chamber can receive process
heat that can be used to increase the temperature of feedstock
materials. For example, irradiating feedstock with radiation (e.g.,
gamma radiation, electron beam radiation, or other types of
radiation) can heat the feedstock materials to relatively high
temperatures. The heated feedstock materials can be cooled by a
heat exchange system that removes some of the excess heat from the
irradiated feedstock. The heat exchange system can be configured to
transport some of the heat energy to the pyrolysis chamber to heat
(or pre-heat) feedstock material, thereby reducing energy cost for
the pyrolysis process.
The slurry containing liquid and solid pyrolysis products can
undergo an optional de-watering step 6070, in which excess water
can be removed from the slurry via processes such as mechanical
pressing and evaporation. The excess water 6280 can be filtered and
then recirculated for further use in quenching the pyrolysis
decomposition products in step 6250.
The de-watered slurry then undergoes a mechanical separation step
6080, in which solid product material 6110 is separated from liquid
product material 6090 by a series of increasingly fine filters. In
step 6100, the liquid product material 6090 can then be condensed
(e.g., via evaporation) to remove waste water 6190, and purified by
processes such as extraction. Extraction can include the addition
of one or more organic solvents 6180, for example, to separate
products such as oils from products such as alcohols. Suitable
organic solvents include, for example, various hydrocarbons and
halo-hydrocarbons. The purified liquid products 6200 can then be
subjected to further processing steps. Waste water 6190 can be
filtered if necessary, and recirculated for further use in
quenching the pyrolysis decomposition products in step 6250.
After separation in step 6080, the solid product material 6110 is
optionally subjected to a drying step 6120 that can include
evaporation of water. Solid material 6110 can then be stored for
later use, or subjected to further processing steps, as
appropriate.
The pyrolysis process parameters discussed above are exemplary. In
general, values of these parameters can vary widely according to
the nature of the feedstock and the desired products. Moreover, a
wide variety of different pyrolysis techniques, including using
heat sources such as hydrocarbon flames and/or furnaces, infrared
lasers, microwave heaters, induction heaters, resistive heaters,
and other heating devices and configurations can be used.
A wide variety of different pyrolysis chambers can be used to
decompose the feedstock. In some embodiments, for example,
pyrolyzing feedstock can include heating the material using a
resistive heating member, such as a metal filament or metal ribbon.
The heating can occur by direct contact between the resistive
heating member and the material.
In certain embodiments, pyrolyzing can include heating the material
by induction, such as by using a Curie-Point pyrolyzer. In some
embodiments, pyrolyzing can include heating the material by the
application of radiation, such as infrared radiation. The radiation
can be generated by a laser, such as an infrared laser.
In certain embodiments, pyrolyzing can include heating the material
with a convective heat. The convective heat can be generated by a
flowing stream of heated gas. The heated gas can be maintained at a
temperature of less than about 1200.degree. C., such as less than
1000.degree. C., less than 750.degree. C., less than 600.degree.
C., less than 400.degree. C. or even less than 300.degree. C. The
heated gas can be maintained at a temperature of greater than about
250.degree. C. The convective heat can be generated by a hot body
surrounding the first material, such as in a furnace.
In some embodiments, pyrolyzing can include heating the material
with steam at a temperature above about 250.degree. C.
An embodiment of a pyrolysis chamber is shown in FIG. 15. Chamber
6500 includes an insulated chamber wall 6510 with a vent 6600 for
exhaust gases, a plurality of burners 6520 that generate heat for
the pyrolysis process, a transport duct 6530 for transporting the
feedstock through chamber 6500, augers 6590 for moving the
feedstock through duct 6530 in a turbulent flow, and a quenching
system 6540 that includes an auger 6610 for moving the pyrolysis
products, water jets 6550 for spraying the pyrolysis products with
cooling water, and a gas separator for separating gaseous products
6580 from a slurry 6570 containing solid and liquid products.
Another embodiment of a pyrolysis chamber is shown in FIG. 16.
Chamber 6700 includes an insulated chamber wall 6710, a feedstock
supply duct 6720, a sloped inner chamber wall 6730, burners 6740
that generate heat for the pyrolysis process, a vent 6750 for
exhaust gases, and a gas separator 6760 for separating gaseous
products 6770 from liquid and solid products 6780. Chamber 6700 is
configured to rotate in the direction shown by arrow 6790 to ensure
adequate mixing and turbulent flow of the feedstock within the
chamber.
A further embodiment of a pyrolysis chamber is shown in FIG. 17.
Filament pyrolyzer 1712 includes a sample holder 1713 with
resistive heating element 1714 in the form of a wire winding
through the open space defined by the sample holder 1713.
Optionally, the heated element can be spun about axis 1715 (as
indicated by arrow 1716) to tumble the material that includes the
cellulosic material in sample holder 1713. The space 1718 defined
by enclosure 1719 is maintained at a temperature above room
temperature, e.g., 200 to 250.degree. C. In a typical usage, a
carrier gas, e.g., an inert gas, or an oxidizing or reducing gas,
traverses through the sample holder 1713 while the resistive
heating element is rotated and heated to a desired temperature,
e.g., 325.degree. C. After an appropriate time, e.g., 5 to 10
minutes, the pyrolyzed material is emptied from the sample holder.
The system shown in FIG. 17 can be scaled and made continuous. For
example, rather than a wire as the heating member, the heating
member can be an auger screw. Material can continuously fall into
the sample holder, striking a heated screw that pyrolizes the
material. At the same time, the screw can push the pyrolyzed
material out of the sample holder to allow for the entry of fresh,
unpyrolyzed material.
Another embodiment of a pyrolysis chamber is shown in FIG. 18,
which features a Curie-Point pyrolyzer 1820 that includes a sample
chamber 1821 housing a ferromagnetic foil 1822. Surrounding the
sample chamber 1821 is an RF coil 1823. The space 1824 defined by
enclosure 1825 is maintained at a temperature above room
temperature, e.g., 200 to 250.degree. C. In a typical usage, a
carrier gas traverses through the sample chamber 1821 while the
foil 1822 is inductively heated by an applied RF field to pyrolize
the material at a desired temperature.
Yet another embodiment of a pyrolysis chamber is shown in FIG. 19.
Furnace pyrolyzer 130 includes a movable sample holder 131 and a
furnace 132. In a typical usage, the sample is lowered (as
indicated by arrow 137) into a hot zone 135 of furnace 132, while a
carrier gas fills the housing 136 and traverses through the sample
holder 131. The sample is heated to the desired temperature for a
desired time to provide a pyrolyzed product. The pyrolyzed product
is removed from the pyrolyzer by raising the sample holder (as
indicated by arrow 134).
In certain embodiments, as shown in FIG. 20, a cellulosic target
140 can be pyrolyzed by treating the target, which is housed in a
vacuum chamber 141, with laser light, e.g., light having a
wavelength of from about 225 nm to about 1500 nm. For example, the
target can be ablated at 266 nm, using the fourth harmonic of a
Nd-YAG laser (Spectra Physics, GCR170, San Jose, Calif.). The
optical configuration shown allows the nearly monochromatic light
143 generated by the laser 142 to be directed using mirrors 144 and
145 onto the target after passing though a lens 146 in the vacuum
chamber 141. Typically, the pressure in the vacuum chamber is
maintained at less than about 10.sup.-6 mm Hg. In some embodiments,
infrared radiation is used, e.g., 1.06 micron radiation from an
Nd-YAG laser. In such embodiments, an infrared sensitive dye can be
combined with the cellulosic material to produce a cellulosic
target. The infrared dye can enhance the heating of the cellulosic
material. Laser ablation is described by Blanchet-Fincher et al.,
in U.S. Pat. No. 5,942,649.
Referring to FIG. 21, in some embodiments, a cellulosic material
can be flash pyrolyzed by coating a tungsten filament 150, such as
a 5 to 25 mil tungsten filament, with the desired cellulosic
material while the material is housed in a vacuum chamber 151. To
affect pyrolysis, current is passed through the filament, which
causes a rapid heating of the filament for a desired time.
Typically, the heating is continued for seconds before allowing the
filament to cool. In some embodiments, the heating is performed a
number of times to effect the desired amount of pyrolysis.
In certain embodiments, carbohydrate-containing biomass material
can be heated in an absence of oxygen in a fluidized bed reactor.
If desired, the carbohydrate containing biomass can have relatively
thin cross-sections, and can include any of the fibrous materials
described herein, for efficient heat transfer. The material can be
heated by thermal transfer from a hot metal or ceramic, such as
glass beads or sand in the reactor, and the resulting pyrolysis
liquid or oil can be transported to a central refinery for making
combustible fuels or other useful products.
In some embodiments, irradiating the biomass material, e.g., with a
beam of particles, such as electrons, prior to pyrolysis can lower
the pyrolysis temperature, resulting in less energy being consumed
during pyrolysis.
Oxidation
One or more oxidative processing sequences can be used to process
raw feedstock from a wide variety of different sources to extract
useful substances from the feedstock, and to provide partially
degraded organic material which functions as input to further
processing steps and/or sequences.
Referring again to FIG. 8, a first material 2 that includes
cellulose having a first number average molecular weight
(.sup.TM.sub.N1) and having a first oxygen content (.sup.TO.sub.1)
is oxidized, e.g., by heating the first material in a tube furnace
in stream of air or oxygen-enriched air, to provide a second
material 3 that includes cellulose having a second number average
molecular weight (.sup.TM.sub.N2) and having a second oxygen
content (.sup.TO.sub.2) higher than the first oxygen content
(.sup.TO.sub.1). The second material (or the first and second
material in certain embodiments) can be, e.g., combined with a
resin, such as a molten thermoplastic resin or a microorganism, to
provide a composite 4 having desirable mechanical properties, or a
fuel 5
Such materials can also be combined with a solid and/or a liquid.
For example, the liquid can be in the form of a solution and the
solid can be particulate in form. The liquid and/or solid can
include a microorganism, e.g., a bacterium, and/or an enzyme. For
example, the bacterium and/or enzyme can work on the cellulosic or
lignocellulosic material to produce a fuel, such as ethanol, or a
coproduct, such as a protein. Fuels and coproducts are described in
FIBROUS MATERIALS AND COMPOSITES," U.S. Ser. No. 11/453,951, filed
Jun. 15, 2006. The entire contents of each of the foregoing
applications are incorporated herein by reference.
In some embodiments, the second number average molecular weight is
not more than 97 percent lower than the first number average
molecular weight, e.g., not more than 95 percent, 90, 85, 80, 75,
70, 65, 60, 55, 50, 45, 40, 30, 20, 12.5, 10.0, 7.5, 5.0, 4.0, 3.0,
2.5, 2.0 or not more than 1.0 percent lower than the first number
average molecular weight. The amount of reduction of molecular
weight will depend upon the application.
In some embodiments in which the materials are used to make a fuel
or a coproduct, the starting number average molecular weight (prior
to oxidation) is from about 200,000 to about 3,200,000, e.g., from
about 250,000 to about 1,000,000 or from about 250,000 to about
700,000, and the number average molecular weight after oxidation is
from about 50,000 to about 200,000, e.g., from about 60,000 to
about 150,000 or from about 70,000 to about 125,000. However, in
some embodiments, e.g., after extensive oxidation, it is possible
to have a number average molecular weight of less than about 10,000
or even less than about 5,000.
In some embodiments, the second oxygen content is at least about
five percent higher than the first oxygen content, e.g., 7.5
percent higher, 10.0 percent higher, 12.5 percent higher, 15.0
percent higher or 17.5 percent higher. In some preferred
embodiments, the second oxygen content is at least about 20.0
percent higher than the oxygen content of the first material.
Oxygen content is measured by elemental analysis by pyrolyzing a
sample in a furnace operating 1300.degree. C. or higher. A suitable
elemental analyzer is the LECO CHNS-932 analyzer with a VTF-900
high temperature pyrolysis furnace.
In some embodiments, oxidation of first material 200 does not
result in a substantial change in the crystallinity of the
cellulose. However, in some instances, e.g., after extreme
oxidation, the second material has cellulose that has as
crystallinity (.sup.TC.sub.2) that is lower than the crystallinity
(.sup.TC.sub.1) of the cellulose of the first material. For
example, (.sup.TC.sub.2) can be lower than (.sup.TC.sub.1) by more
than about 5 percent, e.g., 10, 15, 20, or even 25 percent. This
can be desirable to enhance solubility of the materials in a
liquid, such as a liquid that includes a bacterium and/or an
enzyme.
In some embodiments, the starting crystallinity index (prior to
oxidation) is from about 40 to about 87.5 percent, e.g., from about
50 to about 75 percent or from about 60 to about 70 percent, and
the crystallinity index after oxidation is from about 30 to about
75.0 percent, e.g., from about 35.0 to about 70.0 percent or from
about 37.5 to about 65.0 percent. However, in certain embodiments,
e.g., after extensive oxidation, it is possible to have a
crystallinity index of lower than 5 percent. In some embodiments,
the material after oxidation is substantially amorphous.
Without wishing to be bound by any particular theory, it is
believed that oxidation increases the number of hydrogen-bonding
groups on the cellulose, such as hydroxyl groups, aldehyde groups,
ketone groups carboxylic acid groups or anhydride groups, which can
increase its dispersibility and/or its solubility (e.g., in a
liquid). To further improve dispersibility in a resin, the resin
can include a component that includes hydrogen-bonding groups, such
as one or more anhydride groups, carboxylic acid groups, hydroxyl
groups, amide groups, amine groups or mixtures of any of these
groups. In some preferred embodiments, the component includes a
polymer copolymerized with and/or grafted with maleic anhydride.
Such materials are available from Dupont under the tradename
FUSABOND.RTM..
Generally, oxidation of first material 200 occurs in an oxidizing
environment. For example, the oxidation can be effected or aided by
pyrolysis in an oxidizing environment, such as in air or argon
enriched in air. To aid in the oxidation, various chemical agents,
such as oxidants, acids or bases can be added to the material prior
to or during oxidation. For example, a peroxide (e.g., benzoyl
peroxide) can be added prior to oxidation.
Oxidation Systems
FIG. 22 shows a process flow diagram 5000 that includes various
steps in an oxidative feedstock pretreatment system. In first step
5010, a supply of dry feedstock is received from a feed source. The
feed source can include, for example, a storage bed or container
that is connected to an in-line oxidation reactor via a conveyor
belt or another feedstock transport device.
As described above, the dry feedstock from the feed source may be
pre-processed prior to delivery to the oxidation reactor. For
example, if the feedstock is derived from plant sources, certain
portions of the plant material may be removed prior to collection
of the plant material and/or before the plant material is delivered
by the feedstock transport device. Alternatively, or in addition,
the biomass feedstock can be subjected to mechanical processing
(e.g., to reduce the average length of fibers in the feedstock)
prior to delivery to the oxidation reactor.
Following mechanical processing 5020, feedstock 5030 is transported
to a mixing system which introduces water 5150 into the feedstock
in a mechanical mixing process. Combining water with the processed
feedstock in mixing step 5040 creates an aqueous feedstock slurry
5050, which can then be treated with one or more oxidizing
agents.
Typically, one liter of water is added to the mixture for every
0.02 kg to 1.0 kg of dry feedstock. The ratio of feedstock to water
in the mixture depends upon the source of the feedstock and the
specific oxidizing agents used further downstream in the overall
process. For example, in typical industrial processing sequences
for lignocellulosic biomass, aqueous feedstock slurry 5050 includes
from about 0.5 kg to about 1.0 kg of dry biomass per liter of
water.
In some embodiments, one or more fiber-protecting additives 5170
can also be added to the feedstock slurry in feedstock mixing step
5040. Fiber-protecting additives help to reduce degradation of
certain types of biomass fibers (e.g., cellulose fibers) during
oxidation of the feedstock. Fiber-protecting additives can be used,
for example, if a desired product from processing a lignocellulosic
feedstock includes cellulose fibers. Exemplary fiber-protecting
additives include magnesium compounds such as magnesium hydroxide.
Concentrations of fiber-protecting additives in feedstock slurry
5050 can be from 0.1% to 0.4% of the dry weight of the biomass
feedstock, for example.
In certain embodiments, aqueous feedstock slurry 5050 can be
subjected to an optional extraction 5180 with an organic solvent to
remove water-insoluble substances from the slurry. For example,
extraction of slurry 5050 with one or more organic solvents yields
a purified slurry and an organic waste stream 5210 that includes
water-insoluble materials such as fats, oils, and other non-polar,
hydrocarbon-based substances. Suitable solvents for performing
extraction of slurry 5050 include various alcohols, hydrocarbons,
and halo-hydrocarbons, for example.
In some embodiments, aqueous feedstock slurry 5050 can be subjected
to an optional thermal treatment 5190 to further prepare the
feedstock for oxidation. An example of a thermal treatment includes
heating the feedstock slurry in the presence of pressurized steam.
In fibrous biomass feedstock, the pressurized steam swells the
fibers, exposing a larger fraction of fiber surfaces to the aqueous
solvent and to oxidizing agents that are introduced in subsequent
processing steps.
In certain embodiments, aqueous feedstock slurry 5050 can be
subjected to an optional treatment with basic agents 5200.
Treatment with one or more basic agents can help to separate lignin
from cellulose in lignocellulosic biomass feedstock, thereby
improving subsequent oxidation of the feedstock. Exemplary basic
agents include alkali and alkaline earth hydroxides such as sodium
hydroxide, potassium hydroxide, and calcium hydroxide. In general,
a variety of basic agents can be used, typically in concentrations
from about 0.01% to about 0.5% of the dry weight of the
feedstock.
Aqueous feedstock slurry 5050 is transported (e.g., by an in-line
piping system) to a chamber, which can be an oxidation
preprocessing chamber or an oxidation reactor. In oxidation
preprocessing step 5060, one or more oxidizing agents 5160 are
added to feedstock slurry 5050 to form an oxidizing medium. In some
embodiments, for example, oxidizing agents 5160 can include
hydrogen peroxide. Hydrogen peroxide can be added to slurry 5050 as
an aqueous solution, and in proportions ranging from 3% to between
30% and 35% by weight of slurry 5050. Hydrogen peroxide has a
number of advantages as an oxidizing agent. For example, aqueous
hydrogen peroxide solution is relatively inexpensive, is relatively
chemically stable, and is not particularly hazardous relative to
other oxidizing agents (and therefore does not require burdensome
handling procedures and expensive safety equipment). Moreover,
hydrogen peroxide decomposes to form water during oxidation of
feedstock, so that waste stream cleanup is relatively
straightforward and inexpensive.
In certain embodiments, oxidizing agents 5160 can include oxygen
(e.g., oxygen gas) either alone, or in combination with hydrogen
peroxide. Oxygen gas can be bubbled into slurry 5050 in proportions
ranging from 0.5% to 10% by weight of slurry 5050. Alternatively,
or in addition, oxygen gas can also be introduced into a gaseous
phase in equilibrium with slurry 5050 (e.g., a vapor head above
slurry 5050). The oxygen gas can be introduced into either an
oxidation preprocessing chamber or into an oxidation reactor (or
into both), depending upon the configuration of the oxidative
processing system. Typically, for example, the partial pressure of
oxygen in the vapor above slurry 5050 is larger than the ambient
pressure of oxygen, and ranges from 0.5 bar to 35 bar, depending
upon the nature of the feedstock.
The oxygen gas can be introduced in pure form, or can be mixed with
one or more carrier gases. For example, in some embodiments,
high-pressure air provides the oxygen in the vapor. In certain
embodiments, oxygen gas can be supplied continuously to the vapor
phase to ensure that a concentration of oxygen in the vapor remains
within certain predetermined limits during processing of the
feedstock. In some embodiments, oxygen gas can be introduced
initially in sufficient concentration to oxidize the feedstock, and
then the feedstock can be transported to a closed, pressurized
vessel (e.g., an oxidation reactor) for processing.
In certain embodiments, oxidizing agents 5160 can include nascent
oxygen (e.g., oxygen radicals). Typically, nascent oxygen is
produced as needed in an oxidation reactor or in a chamber in fluid
communication with an oxidation reactor by one or more
decomposition reactions. For example, in some embodiments, nascent
oxygen can be produced from a reaction between NO and O.sub.2 in a
gas mixture or in solution. In certain embodiments, nascent oxygen
can be produced from decomposition of HOCl in solution. Other
methods by which nascent oxygen can be produced include via
electrochemical generation in electrolyte solution, for
example.
In general, nascent oxygen is an efficient oxidizing agent due to
the relatively high reactivity of the oxygen radical. However,
nascent oxygen can also be a relatively selective oxidizing agent.
For example, when lignocellulosic feedstock is treated with nascent
oxygen, selective oxidation of lignin occurs in preference to the
other components of the feedstock such as cellulose. As a result,
oxidation of feedstock with nascent oxygen provides a method for
selective removal of the lignin fraction in certain feedstocks.
Typically, nascent oxygen concentrations of between about 0.5% and
5% of the dry weight of the feedstock are used to effect efficient
oxidation.
Without wishing to be bound by theory, it is believed that nascent
oxygen reacts with lignocellulosic feedstock according to at least
two different mechanisms. In a first mechanism, nascent oxygen
undergoes an addition reaction with the lignin, resulting in
partial oxidation of the lignin, which solubilizes the lignin in
aqueous solution. As a result, the solubilized lignin can be
removed from the rest of the feedstock via washing. In a second
mechanism, nascent oxygen disrupts butane cross-links and/or opens
aromatic rings that are connected via the butane cross-links. As a
result, solubility of the lignin in aqueous solution increases,
facilitating separation of the lignin fraction from the remainder
of the feedstock via washing.
In some embodiments, oxidizing agents 5160 include ozone (O.sub.3).
The use of ozone can introduce several chemical handling
considerations in the oxidation processing sequence. If heated too
vigorously, an aqueous solution of ozone can decompose violently,
with potentially adverse consequences for both human system
operators and system equipment. Accordingly, ozone is typically
generated in a thermally isolated, thick-walled vessel separate
from the vessel that contains the feedstock slurry, and transported
thereto at the appropriate process stage.
Without wishing to be bound by theory, it is believed that ozone
decomposes into oxygen and oxygen radicals, and that the oxygen
radicals (e.g., nascent oxygen) are responsible for the oxidizing
properties of ozone in the manner discussed above. Ozone typically
preferentially oxidizes the lignin fraction in lignocellulosic
materials, leaving the cellulose fraction relatively
undisturbed.
Conditions for ozone-based oxidation of biomass feedstock generally
depend upon the nature of the biomass. For example, for cellulosic
and/or lignocellulosic feedstocks, ozone concentrations of from 0.1
g/m.sup.3 to 20 g/m.sup.3 of dry feedstock provide for efficient
feedstock oxidation. Typically, the water content in slurry 5050 is
between 10% by weight and 80% by weight (e.g., between 40% by
weight and 60% by weight). During ozone-based oxidation, the
temperature of slurry 5050 can be maintained between 0.degree. C.
and 100.degree. C. to avoid violent decomposition of the ozone.
In some embodiments, feedstock slurry 5050 can be treated with an
aqueous, alkaline solution that includes one or more alkali and
alkaline earth hydroxides such as sodium hydroxide, potassium
hydroxide, and calcium hydroxide, and then treated thereafter with
an ozone-containing gas in an oxidation reactor. This process has
been observed to significantly increase decomposition of the
biomass in slurry 5050. Typically, for example, a concentration of
hydroxide ions in the alkaline solution is between 0.001% and 10%
by weight of slurry 5050. After the feedstock has been wetted via
contact with the alkaline solution, the ozone-containing gas is
introduced into the oxidation reactor, where it contacts and
oxidizes the feedstock.
Oxidizing agents 5160 can also include other substances. In some
embodiments, for example, halogen-based oxidizing agents such as
chlorine and oxychlorine agents (e.g., hypochlorite) can be
introduced into slurry 5050. In certain embodiments,
nitrogen-containing oxidizing substances can be introduced into
slurry 5050. Exemplary nitrogen-containing oxidizing substances
include NO and NO.sub.2, for example. Nitrogen-containing agents
can also be combined with oxygen in slurry 5050 to create
additional oxidizing agents. For example, NO and NO.sub.2 both
combine with oxygen in slurry 5050 to form nitrate compounds, which
are effective oxidizing agents for biomass feedstock. Halogen- and
nitrogen-based oxidizing agents can, in some embodiments, cause
bleaching of the biomass feedstock, depending upon the nature of
the feedstock. The bleaching may be desirable for certain
biomass-derived products that are extracted in subsequent
processing steps.
Other oxidizing agents can include, for example, various
peroxyacids, peroxyacetic acids, persulfates, percarbonates,
permanganates, osmium tetroxide, and chromium oxides.
Following oxidation preprocessing step 5060, feedstock slurry 5050
is oxidized in step 5070. If oxidizing agents 5160 were added to
slurry 5050 in an oxidation reactor, then oxidation proceeds in the
same reactor. Alternatively, if oxidizing agents 5160 were added to
slurry 5050 in a preprocessing chamber, then slurry 5050 is
transported to an oxidation reactor via an in-line piping system.
Once inside the oxidation reactor, oxidation of the biomass
feedstock proceeds under a controlled set of environmental
conditions. Typically, for example, the oxidation reactor is a
cylindrical vessel that is closed to the external environment and
pressurized. Both batch and continuous operation is possible,
although environmental conditions are typically easier to control
in in-line batch processing operations.
Oxidation of feedstock slurry 5050 typically occurs at elevated
temperatures in the oxidation reactor. For example, the temperature
of slurry 5050 in the oxidation reactor is typically maintained
above 100.degree. C., e.g., in a range from 120.degree. C. to
240.degree. C. For many types of biomass feedstock, oxidation is
particularly efficient if the temperature of slurry 5050 is
maintained between 150.degree. C. and 220.degree. C. Slurry 5050
can be heating using a variety of thermal transfer devices. For
example, in some embodiments, the oxidation reactor contacts a
heating bath that includes oil or molten salts. In certain
embodiments, a series of heat exchange pipes surround and contact
the oxidation reactor, and circulation of hot fluid within the
pipes heats slurry 5050 in the reactor. Other heating devices that
can be used to heat slurry 5050 include resistive heating elements,
induction heaters, and microwave sources, for example.
The residence time of feedstock slurry 5050 in the oxidation
reactor can be varied as desired to process the feedstock.
Typically, slurry 5050 spends from 1 minute to 60 minutes
undergoing oxidation in the reactor. For relatively soft biomass
material such as lignocellulosic matter, the residence time in the
oxidation reactor can be from 5 minutes to 30 minutes, for example,
at an oxygen pressure of between 3 and 12 bars in the reactor, and
at a slurry temperature of between 160.degree. C. and 210.degree.
C. For other types of feedstock, however, residence times in the
oxidation reactor can be longer, e.g., as long 48 hours. To
determine appropriate residence times for slurry 5050 in the
oxidation reactor, aliquots of the slurry can be extracted from the
reactor at specific intervals and analyzed to determine
concentrations of particular products of interest such as complex
saccharides. Information about the increase in concentrations of
certain products in slurry 5050 as a function of time can be used
to determine residence times for particular classes of feedstock
material.
In some embodiments, during oxidation of feedstock slurry 5050,
adjustment of the slurry pH may be performed by introducing one or
more chemical agents into the oxidation reactor. For example, in
certain embodiments, oxidation occurs most efficiently in a pH
range of about 9-11. To maintain a pH in this range, agents such as
alkali and alkaline earth hydroxides, carbonates, ammonia, and
alkaline buffer solutions can be introduced into the oxidation
reactor.
Circulation of slurry 5050 during oxidation can be important to
ensure sufficient contact between oxidizing agents 5160 and the
feedstock. Circulation of the slurry can be achieved using a
variety of techniques. For example, in some embodiments, a
mechanical stirring apparatus that includes impeller blades or a
paddle wheel can be implemented in the oxidation reactor. In
certain embodiments, the oxidation reactor can be a loop reactor,
in which the aqueous solvent in which the feedstock is suspended is
simultaneously drained from the bottom of the reactor and
recirculated into the top of the reactor via pumping, thereby
ensuring that the slurry is continually re-mixed and does not
stagnate within the reactor.
After oxidation of the feedstock is complete, the slurry is
transported to a separation apparatus where a mechanical separation
step 5080 occurs. Typically, mechanical separation step 5080
includes one or more stages of increasingly fine filtering of the
slurry to mechanically separate the solid and liquid
constituents.
Liquid phase 5090 is separated from solid phase 5100, and the two
phases are processed independently thereafter. Solid phase 5100 can
optionally undergo a drying step 5120 in a drying apparatus, for
example. Drying step 5120 can include, for example, mechanically
dispersing the solid material onto a drying surface, and
evaporating water from solid phase 5100 by gentle heating of the
solid material. Following drying step 5120 (or, alternatively,
without undergoing drying step 5120), solid phase 5100 is
transported for further processing steps 5140.
Liquid phase 5090 can optionally undergo a drying step 5110 to
reduce the concentration of water in the liquid phase. In some
embodiments, for example, drying step 5110 can include evaporation
and/or distillation and/or extraction of water from liquid phase
5090 by gentle heating of the liquid. Alternatively, or in
addition, one or more chemical drying agents can be used to remove
water from liquid phase 5090. Following drying step 5110 (or
alternatively, without undergoing drying step 5110), liquid phase
5090 is transported for further processing steps 5130, which can
include a variety of chemical and biological treatment steps such
as chemical and/or enzymatic hydrolysis.
Drying step 5110 creates waste stream 5220, an aqueous solution
that can include dissolved chemical agents such as acids and bases
in relatively low concentrations. Treatment of waste stream 5220
can include, for example, pH neutralization with one or more
mineral acids or bases. Depending upon the concentration of
dissolved salts in waste stream 5220, the solution may be partially
de-ionized (e.g., by passing the waste stream through an ion
exchange system). Then, the waste stream--which includes primarily
water--can be re-circulated into the overall process (e.g., as
water 5150), diverted to another process, or discharged.
Typically, for lignocellulosic biomass feedstocks following
separation step 5070, liquid phase 5090 includes a variety of
soluble poly- and oligosaccharides, which can then be separated
and/or reduced to smaller-chain saccharides via further processing
steps. Solid phase 5100 typically includes primarily cellulose, for
example, with smaller amounts of hemicellulose- and lignin-derived
products.
In some embodiments, oxidation can be carried out at elevated
temperature in a reactor such as a pyrolysis chamber. For example,
referring again to FIG. 17, feedstock materials can be oxidized in
filament pyrolyzer 1712. In a typical usage, an oxidizing carrier
gas, e.g., air or an air/argon blend, traverses through the sample
holder 1713 while the resistive heating element is rotated and
heated to a desired temperature, e.g., 325.degree. C. After an
appropriate time, e.g., 5 to 10 minutes, the oxidized material is
emptied from the sample holder. The system shown in FIG. 17 can be
scaled and made continuous. For example, rather than a wire as the
heating member, the heating member can be an auger screw. Material
can continuously fall into the sample holder, striking a heated
screw that pyrolizes the material. At the same time, the screw can
push the oxidized material out of the sample holder to allow for
the entry of fresh, unoxidized material.
Feedstock materials can also be oxidized in any of the pyrolysis
systems shown in FIGS. 18-20 and described above in the Pyrolysis
Systems section.
Referring again to FIG. 21, feedstock materials can be rapidly
oxidized by coating a tungsten filament 150, together with an
oxidant, such as a peroxide, with the desired cellulosic material
while the material is housed in a vacuum chamber 151. To affect
oxidation, current is passed through the filament, which causes a
rapid heating of the filament for a desired time. Typically, the
heating is continued for seconds before allowing the filament to
cool. In some embodiments, the heating is performed a number of
times to effect the desired amount of oxidation.
Referring again to FIG. 12, in some embodiments, feedstock
materials can be oxidized with the aid of sound and/or cavitation.
Generally, to effect oxidation, the materials are sonicated in an
oxidizing environment, such as water saturated with oxygen or
another chemical oxidant, such as hydrogen peroxide.
Referring again to FIGS. 9 and 10, in certain embodiments, ionizing
radiation is used to aid in the oxidation of feedstock materials.
Generally, to effect oxidation, the materials are irradiated in an
oxidizing environment, such as air or oxygen. For example, gamma
radiation and/or electron beam radiation can be employed to
irradiate the materials.
Other Processes
Steam explosion can be used alone without any of the processes
described herein, or in combination with any one or more of the
processes described herein.
FIG. 23 shows an overview of the entire process of converting a
fiber source or feedstock 400 into a product 450, such as ethanol,
by a process that includes shearing and steam explosion to produce
a fibrous material 401, which is then hydrolyzed and converted,
e.g., fermented, to produce the product. The fiber source can be
transformed into the fibrous material 401 through a number of
possible methods, including at least one shearing process and at
least one steam explosion process.
For example, one option includes shearing the fiber source,
followed by optional screening step(s) and optional additional
shearing step(s) to produce a sheared fiber source 402, which can
then be steam exploded to produce the fibrous material 401. The
steam explosion process is optionally followed by a fiber recovery
process to remove liquids or the "liquor" 404, resulting from the
steam exploding process. The material resulting from steam
exploding the sheared fiber source may be further sheared by
optional additional shearing step(s) and/or optional screening
step(s).
In another method, the fibrous material 401 is first steam exploded
to produce a steam exploded fiber source 410. The resulting steam
exploded fiber source is then subjected to an optional fiber
recovery process to remove liquids, or the liquor. The resulting
steam exploded fiber source can then be sheared to produce the
fibrous material. The steam exploded fiber source can also be
subject to one or more optional screening steps and/or one or more
optional additional shearing steps. The process of shearing and
steam exploding the fiber source to produce the sheared and steam
exploded fibrous material will be further discussed below.
The fiber source can be cut into pieces or strips of confetti
material prior to shearing or steam explosion. The shearing
processes can take place with the material in a dry state (e.g.,
having less than 0.25 percent by weight absorbed water), a hydrated
state, or even while the material is partially or fully submerged
in a liquid, such as water or isopropanol. The process can also
optimally include steps of drying the output after steam exploding
or shearing to allow for additional steps of dry shearing or steam
exploding. The steps of shearing, screening, and steam explosion
can take place with or without the presence of various chemical
solutions.
In a steam explosion process, the fiber source or the sheared fiber
source is contacted with steam under high pressure, and the steam
diffuses into the structures of the fiber source (e.g., the
lignocellulosic structures). The steam then condenses under high
pressure thereby "wetting" the fiber source. The moisture in the
fiber source can hydrolyze any acetyl groups in the fiber source
(e.g., the acetyl groups in the hemicellulose fractions), forming
organic acids such as acetic and uronic acids. The acids, in turn,
can catalyze the depolymerization of hemicellulose, releasing xylan
and limited amounts of glucan. The "wet" fiber source (or sheared
fiber source, etc.) is then "exploded" when the pressure is
released. The condensed moisture instantaneously evaporates due to
the sudden decrease in pressure and the expansion of the water
vapor exerts a shear force upon the fiber source (or sheared fiber
source, etc.). A sufficient shear force will cause the mechanical
breakdown of the internal structures (e.g., the lignocellulosic
structures) of the fiber source.
The sheared and steam exploded fibrous material is then converted
into a useful product, such as ethanol. In some embodiments, the
fibrous material is converted into a fuel. One method of converting
the fibrous material into a fuel is by hydrolysis to produce
fermentable sugars, 412, which are then fermented to produce the
product. Other methods of converting fibrous materials into fuels
may also be used.
In some embodiments, prior to combining with the microorganism, the
sheared and steam exploded fibrous material 401 is sterilized to
kill any competing microorganisms that may be on the fibrous
material. For example, the fibrous material can be sterilized by
exposing the fibrous material to radiation, such as infrared
radiation, ultraviolet radiation, or an ionizing radiation, such as
gamma radiation. The microorganisms can also be killed using
chemical sterilants, such as bleach (e.g., sodium hypochlorite),
chlorhexidine, or ethylene oxide.
One method to hydrolyze the sheared and steam exploded fibrous
material is by the use of cellulases. Cellulases are a group of
enzymes that act synergistically to hydrolyze cellulose.
Commercially available Accellerase.RTM. 1000 enzyme complex, which
contains a complex of enzymes that reduces lignocellulosic biomass
into fermentable sugars, can also be used.
According to current understanding, the components of cellulase
include endoglucanases, exoglucanases (cellobiohydrolases), and
b-glucosidases (cellobiases). Synergism between the cellulase
components exists when hydrolysis by a combination of two or more
components exceeds the sum of the activities expressed by the
individual components. The generally accepted mechanism of action
of a cellulase system (particularly of T. longibrachiatum) on
crystalline cellulose is that endoglucanase hydrolyzes internal
.beta.-1,4-glycosidic bonds of the amorphous regions, thereby
increasing the number of exposed non-reducing ends. Exoglucanases
then cleave off cellobiose units from the non-reducing ends, which
in turn are hydrolyzed to individual glucose units by
b-glucosidases. There are several configurations of both endo- and
exo-glucanases differing in stereospecificities. In general, the
synergistic action of the components in various configurations is
required for optimum cellulose hydrolysis. Cellulases, however, are
more inclined to hydrolyze the amorphous regions of cellulose. A
linear relationship between crystallinity and hydrolysis rates
exists whereby higher crystallinity indices correspond to slower
enzyme hydrolysis rates. Amorphous regions of cellulose hydrolyze
at twice the rate of crystalline regions. The hydrolysis of the
sheared and steam exploded fibrous material may be performed by any
hydrolyzing biomass process.
Steam explosion of biomass sometimes causes the formation of
by-products, e.g., toxicants, that are inhibitory to microbial and
enzymatic activities. The process of converting the sheared and
steam exploded fibrous material into a fuel can therefore
optionally include an overliming step prior to fermentation to
precipitate some of the toxicants. For example, the pH of the
sheared and steam exploded fibrous material may be raised to exceed
the pH of 10 by adding calcium hydroxide (Ca(OH).sub.2) followed by
a step of lowering the pH to about 5 by adding H.sub.2SO.sub.4. The
overlimed fibrous material may then be used as is without the
removal of precipitates. As shown in FIG. 23, the optional
overliming step occurs just prior to the step of hydrolysis of the
sheared and steam exploded fibrous material, but it is also
contemplated to perform the overliming step after the hydrolysis
step and prior to the fermenting step.
FIG. 24 depicts an example of a steam explosion apparatus 460. The
steam explosion apparatus 460 includes a reaction chamber 462, in
which the fiber source and/or the fibrous material is placed
through a fiber source inlet 464. The reaction chamber is sealed by
closing fiber source inlet valve 465. The reaction chamber further
includes a pressurized steam inlet 466 that includes a steam valve
467. The reaction chamber further includes an explosive
depressurization outlet 468 that includes an outlet valve 469 in
communication with the cyclone 470 through the connecting pipe 472.
Once the reaction chamber contains the fiber source and/or sheared
fiber source and is sealed by closing valves 465, 467 and 469,
steam is delivered into the reaction chamber 462 by opening the
steam inlet valve 467 allowing steam to travel through steam inlet
466. Once the reaction chamber reaches target temperature, which
can take about 20-60 seconds, the holding time begins. The reaction
chamber is held at the target temperature for the desired holding
time, which typically lasts from about 10 seconds to 5 minutes. At
the end of the holding time period, outlet valve is opened to allow
for explosive depressurization to occur. The process of explosive
depressurization propels the contents of the reaction chamber 462
out of the explosive depressurization outlet 468, through the
connecting pipe 472, and into the cyclone 470. The steam exploded
fiber source or fibrous material then exits the cyclone in a sludge
form into the collection bin 474 as much of the remaining steam
exits the cyclone into the atmosphere through vent 476. The steam
explosion apparatus further includes wash outlet 478 with wash
outlet valve 479 in communication with connecting pipe 472. The
wash outlet valve 479 is closed during the use of the steam
explosion apparatus 460 for steam explosion, but opened during the
washing of the reaction chamber 462.
The target temperature of the reaction chamber 462 is preferably
between 180 and 240 degrees Celsius or between 200 and 220 degrees
Celsius. The holding time is preferably between 10 seconds and 30
minutes, or between 30 seconds and 10 minutes, or between 1 minute
and 5 minutes.
Because the steam explosion process results in a sludge of steam
exploded fibrous material, the steam exploded fibrous material may
optionally include a fiber recovery process where the "liquor" is
separated from the steam exploded fibrous material. This fiber
recovery step is helpful in that it enables further shearing and/or
screening processes and can allow for the conversion of the fibrous
material into fuel. The fiber recovery process occurs through the
use of a mesh cloth to separate the fibers from the liquor. Further
drying processes can also be included to prepare the fibrous
material or steam exploded fiber source for subsequent
processing.
Combined Irradiating, Pyrolyzing, Sonicating, and/or Oxidizing
Devices
In some embodiments, it may be advantageous to combine two or more
separate irradiation, sonication, pyrolization, and/or oxidation
devices into a single hybrid machine. Using such a hybrid machine,
multiple processes may be performed in close juxtaposition or even
simultaneously, with the benefit of increasing pretreatment
throughput and potential cost savings.
For example, consider the electron beam irradiation and sonication
processes. Each separate process is effective in lowering the mean
molecular weight of cellulosic material by an order of magnitude or
more, and by several orders of magnitude when performed
serially.
Both irradiation and sonication processes can be applied using a
hybrid electron beam/sonication device as is illustrated in FIG.
25. Hybrid electron beam/sonication device 2500 is pictured above a
shallow pool (depth .about.3-5 cm) of a slurry of cellulosic
material 2550 dispersed in an aqueous, oxidant medium, such as
hydrogen peroxide or carbamide peroxide. Hybrid device 2500 has an
energy source 2510, which powers both electron beam emitter 2540
and sonication horns 2530.
Electron beam emitter 2540 generates electron beams, which pass
though an electron beam aiming device 2545 to impact the slurry
2550 containing cellulosic material. The electron beam aiming
device can be a scanner that sweeps a beam over a range of up to
about 6 feet in a direction approximately parallel to the surface
of the slurry 2550.
On either side of the electron beam emitter 2540 are sonication
horns 2530, which deliver ultrasonic wave energy to the slurry
2550. The sonication horns 2530 end in a detachable endpiece 2535
that is in contact with the slurry 2550.
The sonication horns 2530 are at risk of damage from long-term
residual exposure to the electron beam radiation. Thus, the horns
can be protected with a standard shield 2520, e.g., made of lead or
a heavy-metal-containing alloy such as Lipowitz metal, which is
impervious to electron beam radiation. Precautions must be taken,
however, to ensure that the ultrasonic energy is not affected by
the presence of the shield. The detachable endpieces 2535, which
are constructed of the same material and attached to the horns
2530, are in contact with the cellulosic material 2550 during
processing and are expected to be damaged. Accordingly, the
detachable endpieces 2535 are constructed to be easily
replaceable.
A further benefit of such a simultaneous electron beam and
ultrasound process is that the two processes have complementary
results. With electron beam irradiation alone, an insufficient dose
may result in cross-linking of some of the polymers in the
cellulosic material, which lowers the efficiency of the overall
depolymerization process. Lower doses of electron beam irradiation
and/or ultrasound radiation may also be used to achieve a similar
degree of depolymerization as that achieved using electron beam
irradiation and sonication separately. An electron beam device can
also be combined with one or more of high frequency, rotor-stator
devices, which can be used as an alternative to ultrasonic
sonication devices.
Further combinations of devices are also possible. For example, an
ionizing radiation device that produces gamma radiation emitted
from, e.g., .sup.60Co pellets, can be combined with an electron
beam source and/or an ultrasonic wave source. Shielding
requirements may be more stringent in this case.
The radiation devices for pretreating biomass discussed above can
also be combined with one or more devices that perform one or more
pyrolysis processing sequences. Such a combination may again have
the advantage of higher throughput. Nevertheless, caution must be
observed, as there may be conflicting requirements between some
radiation processes and pyrolysis. For example, ultrasonic
radiation devices may require the feedstock be immersed in a liquid
oxidizing medium. On the other hand, as discussed previously, it
may be advantageous for a sample of feedstock undergoing pyrolysis
to be of a particular moisture content. In this case, the new
systems automatically measure and monitor for a particular moisture
content and regulate the same. Further, some or all of the above
devices, especially the pyrolysis device, can be combined with an
oxidation device as discussed previously.
Primary Processes
Fermentation
Generally, various microorganisms can produce a number of useful
products, such as a fuel, by operating on, e.g., fermenting the
pretreated biomass materials. For example, alcohols, organic acids,
hydrocarbons, hydrogen, proteins or mixtures of any of these
materials can be produced by fermentation or other processes.
The microorganism can be a natural microorganism or an engineered
microorganism. For example, the microorganism can be a bacterium,
e.g., a cellulolytic bacterium, a fungus, e.g., a yeast, a plant or
a protist, e.g., an algae, a protozoa or a fungus-like protist,
e.g., a slime mold. When the organisms are compatible, mixtures of
organisms can be utilized.
To aid in the breakdown of the materials that include the
cellulose, one or more enzymes, e.g., a cellulolytic enzyme can be
utilized. In some embodiments, the materials that include the
cellulose are first treated with the enzyme, e.g., by combining the
material and the enzyme in an aqueous solution. This material can
then be combined with the microorganism. In other embodiments, the
materials that include the cellulose, the one or more enzymes and
the microorganism are combined at the concurrently, e.g., by
combining in an aqueous solution.
Also, to aid in the breakdown of the materials that include the
cellulose, the materials can be treated post irradiation with heat,
a chemical (e.g., mineral acid, base or a strong oxidizer such as
sodium hypochlorite), and/or an enzyme.
During the fermentation, sugars released from cellulolytic
hydrolysis or the saccharification step, are fermented to, e.g.,
ethanol, by a fermenting microorganism such as yeast. Suitable
fermenting microorganisms have the ability to convert
carbohydrates, such as glucose, xylose, arabinose, mannose,
galactose, oligosaccharides or polysaccharides into fermentation
products. Fermenting microorganisms include strains of the genus
Sacchromyces spp. e.g., Sacchromyces cerevisiae (baker's yeast),
Saccharomyces distaticus, Saccharomyces uvarum; the genus
Kluyveromyces, e.g., species Kluyveromyces marxianus, Kluyveromyces
fragilis; the genus Candida, e.g., Candida pseudotropicalis, and
Candida brassicae, Pichia stipitis (a relative of Candida shehatae,
the genus Clavispora, e.g., species Clavispora lusitaniae and
Clavispora opuntiae the genus Pachysolen, e.g., species Pachysolen
tannophilus, the genus Bretannomyces, e.g., species Bretannomyces
clausenii (Philippidis, G. P., 1996, Cellulose bioconversion
technology, in Handbook on Bioethanol: Production and Utilization,
Wyman, C. E., ed., Taylor & Francis, Washington, D.C.,
179-212). In particular embodiments, such as when xylose is
present, Pichia stipitis (ATCC 66278) is utilized in
fermentation.
Commercially available yeast include, for example, Red
Star.RTM./Lesaffre Ethanol Red (available from Red Star/Lesaffre,
USA) FALI.RTM. (available from Fleischmann's Yeast, a division of
Burns Philip Food Inc., USA), SUPERSTART.RTM. (available from
Alltech, now Lallemand), GERT STRAND.RTM. (available from Gert
Strand A B, Sweden) and FERMOL.RTM. (available from DSM
Specialties).
Bacteria that can ferment biomass to ethanol and other products
include, e.g., Zymomonas mobilis and Clostridium thermocellum
(Philippidis, 1996, supra). Leschine et al. (International Journal
of Systematic and Evolutionary Microbiology 2002, 52, 1155-1160)
isolated an anaerobic, mesophilic, cellulolytic bacterium from
forest soil, Clostridium phytofermentans sp. nov., which converts
cellulose to ethanol.
Fermentation of biomass to ethanol and other products may be
carried out using certain types of thermophilic or genetically
engineered microorganisms, such Thermoanaerobacter species,
including T. mathranii, and yeast species such as Pichia species.
An example of a strain of T. mathranii is A3M4 described in
Sonne-Hansen et al. (Applied Microbiology and Biotechnology 1993,
38, 537-541) or Ahring et al. (Arch. Microbiol. 1997, 168,
114-119). Other genetically engineered microorganisms are discussed
in U.S. Pat. No. 7,192,772.
Yeast and Zymomonas bacteria can be used for fermentation or
conversion. The optimum pH for yeast is from about pH 4 to 5, while
the optimum pH for Zymomonas is from about pH 5 to 6. Typical
fermentation times are about 24 to 96 hours with temperatures in
the range of 26.degree. C. to 40.degree. C., however thermophilic
microorganisms prefer higher temperatures.
Enzymes which break down biomass, such as cellulose, to lower
molecular weight carbohydrate-containing materials, such as
glucose, during saccharification are referred to as cellulolytic
enzymes or cellulase. These enzymes may be a complex of enzymes
that act synergistically to degrade crystalline cellulose. Examples
of cellulolytic enzymes include: endoglucanases,
cellobiohydrolases, and cellobiases (.beta.-glucosidases). A
cellulosic substrate is initially hydrolyzed by endoglucanases at
random locations producing oligomeric intermediates. These
intermediates are then substrates for exo-splitting glucanases such
as cellobiohydrolase to produce cellobiose from the ends of the
cellulose polymer. Cellobiose is a water-soluble .beta.-1,4-linked
dimer of glucose. Finally cellobiase cleaves cellobiose to yield
glucose.
A cellulase is capable of degrading biomass and may be of fungal or
bacterial origin. Suitable enzymes include cellulases from the
genera Bacillus, Pseudomonas, Humicola, Fusarium, Thielavia,
Acremonium, Chrysosporium and Trichoderma, and include species of
Humicola, Coprinus, Thielavia, Fusarium, Myceliophthora,
Acremonium, Cephalosporium, Scytalidium, Penicillium or Aspergillus
(see, e.g., EP 458162), especially those produced by a strain
selected from the species Humicola insolens (reclassified as
Scytalidium thermophilum, see, e.g., U.S. Pat. No. 4,435,307),
Coprinus cinereas, Fusarium oxysporum, Myceliophthora thermophile,
Meripilus giganteus, Thielavia terrestris, Acremonium sp.,
Acremonium persicinum, Acremonium acremonium, Acremonium
brachypenium, Acremonium dichromosporum, Acremonium obclavatum,
Acremonium pinkertoniae, Acremonium roseogriseum, Acremonium
incoloratum, and Acremonium furatum; preferably from the species
Humicola insolens DSM 1800, Fusarium oxysporum DSM 2672,
Myceliophthora thermophila CBS117.65, Cephalosporium sp. RYM-202,
Acremonium sp. CBS 478.94, Acremonium sp. CBS 265.95, Acremonium
persicinum CBS169.65, Acremonium acremonium AHU 9519,
Cephalosporium sp. CBS 535.71, Acremonium brachypenium CBS 866.73,
Acremonium dichromosporum CBS 683.73, Acremonium obclavatum CBS
311.74, Acremonium pinkertoniae CBS157.70, Acremonium roseogriseum
CBS134.56, Acremonium incoloratum CBS146.62, and Acremonium furatum
CBS 299.70H. Cellulolytic enzymes may also be obtained from
Chrysosporium, preferably a strain of Chrysosporium lucknowense.
Additionally, Trichoderma (particularly Trichoderma viride,
Trichoderma reesei, and Trichoderma koningii), alkalophilic
Bacillus (see, for example, U.S. Pat. No. 3,844,890 and EP 458162),
and Streptomyces (see, e.g., EP 458162) may be used. The bacterium,
Saccharophagus degradans, produces a mixture of enzymes capable of
degrading a range of cellulosic materials and may also be used in
this process.
Anaerobic cellulolytic bacteria have also been isolated from soil,
e.g., a novel cellulolytic species of Clostridium, Clostridium
phytofermentans sp. nov. (see Leschine et. al, International
Journal of Systematic and Evolutionary Microbiology (2002), 52,
1155-1160).
Cellulolytic enzymes using recombinant technology can also be used
(see, e.g., WO 2007/071818 and WO 2006/110891).
Other enzyme and enzyme formulations that can be used are discussed
in Published U.S. Patent Application Nos. 2006/0008885 and
2006/0068475, and in PCT Application No. WO 2006/128304.
The cellulolytic enzymes used can be produced by fermentation of
the above-noted microbial strains on a nutrient medium containing
suitable carbon and nitrogen sources and inorganic salts, using
procedures known in the art (see, e.g., Bennett, J. W. and LaSure,
L. (eds.), More Gene Manipulations in Fungi, Academic Press, CA
1991). Suitable media are available from commercial suppliers or
may be prepared according to published compositions (e.g., in
catalogues of the American Type Culture Collection). Temperature
ranges and other conditions suitable for growth and cellulase
production are known in the art (see, e.g., Bailey, J. E., and 011
is, D. F., Biochemical Engineering Fundamentals, McGraw-Hill Book
Company, NY, 1986).
Treatment of cellulose with cellulase is usually carried out at
temperatures between 30.degree. C. and 65.degree. C. Cellulases are
active over a range of pH of about 3 to 7. A saccharification step
may last up to 120 hours. The cellulase enzyme dosage achieves a
sufficiently high level of cellulose conversion. For example, an
appropriate cellulase dosage is typically between 5.0 and 50 Filter
Paper Units (FPU or IU) per gram of cellulose. The FPU is a
standard measurement and is defined and measured according to Ghose
(1987, Pure and Appl. Chem. 59:257-268).
In particular embodiments, ACCELERASE.RTM. 1000 enzyme complex
(Genencor) is utilized as the enzyme system at a loading of 0.25 mL
per gram of substrate. ACCELERASE.RTM. 1000 enzyme complex is a
multiple enzyme cocktail with multiple activities, mainly
exoglucanase, endoglucanase, hemicellulase and beta-glucosidase.
The cocktail has a minimum endoglucanase activity of 2500 CMC U/g
and a minimum beta-glucosidase activity of 400 pNPG U/g. The pH of
the cocktail is from about 4.8 to about 5.2. In other particular
embodiments, the enzyme system utilized is a blend of
CELLUCLAST.RTM. 1.5 L and Novozyme 188. For example, 0.5 mL of
CELLUCLAST.RTM. 1.5 L and 0.1 mL of Novozyme 188 can be used for
each gram of substrate. When a higher hemicellulase (xylanase)
activity is desired, OPTIMASH.TM. BG can be utilized.
Mobile fermentors can be utilized, as described in U.S. Provisional
Patent Application Ser. 60/832,735, now Published International
Application No. WO 2008/011598.
Ethanol Fermentation
Ethanol is a product of fermentation. Fermentation is a sequence of
reactions which release energy from organic molecules in the
absence of oxygen. In this application of fermentation, energy is
obtained when sugar is changed to ethanol and carbon dioxide. All
beverage ethanol, and more than half of industrial ethanol, is made
by this process. Changing corn to ethanol by fermentation takes
many steps. Starch in corn must be broken down into simple sugars
before fermentation can occur. This can be achieved, for example,
by cooking the corn and adding the enzymes alpha amylase and gluco
amylase. These enzymes function as catalysts to speed up the
chemical changes. Once a simple sugar is obtained, yeast is added.
Yeast is a single-celled fungus, which feeds on the sugar and
causes the fermentation. As the fungi feeds on the sugar, it
produces alcohol (ethanol) and carbon dioxide. In fermentation, the
ethanol retains much of the energy that was originally in the
sugar, which explains why ethanol is an excellent fuel.
The fermentation reaction is represented by the simple equation:
C.sub.6H.sub.12O.sub.6.fwdarw.2CH.sub.3CH.sub.2OH+2CO.sub.2
Ethanol can be made from a wide variety of available feedstocks.
Fuel ethanol can be made from crops which contain starch such as
feed grains, food grains, such as corn, and tubers, such as
potatoes and sweet potatoes. Crops containing sugar, such as sugar
beets, sugarcane, and sweet sorghum also could be used for the
production of ethanol. In addition, food processing byproducts,
such as molasses, cheese whey, and cellulosic materials including
grass and wood, as well as agricultural and forestry residues, can
be processed to ethanol. As discussed above, these and other
feedstocks can be treated as discussed herein to facilitate
production of ethanol.
Conversion of Starchy Materials
FIGS. 26 and 27 show block diagrams for a dry and wet milling
process, respectively, and illustrate the conversion, e.g.,
fermentation, of corn kernels to ethanol and other valuable
co-products.
Referring particularly now to FIG. 26, in some implementations, a
dry milling process for the conversion of corn kernels to ethanol,
e.g., anhydrous ethanol, that can be utilized as a fuel, e.g.,
automobile or aviation fuel, can begin with pretreating the dried
corn kernels with any one or more pretreatments described herein,
such as radiation, e.g., any one or more types of radiation
described herein (e.g., a beam of electrons in which each electron
has an energy of about 5 MeV or a beam of protons in which the
energy of each proton is about 3-100 MeV). After pre-treatment, the
corn kernels can be ground and/or sheared into a powder. Although
any one or more pretreatments described herein can be applied after
grinding and/or at any time during the dry milling process outlined
in FIG. 26, pretreating prior to grinding and/or shearing can be
advantageous in that the kernels are generally more brittle after
pretreatment and, as a result, are easier and can require less
energy to grind and/or shear. In some embodiments, a selected
pretreatment can be applied more than once during conversion, e.g.,
prior to milling and then after milling.
After grinding and/or shearing, the milled, dry kernels can be
optionally hydrated by adding the milled material to a vessel
containing water and, optionally, hydrating agents, such as
surfactants. Optionally, this reaction vessel can also include one
or more enzymes, such as amylase, to aid in further breakdown of
starchy biomass, or the reaction vessel may contain one or more
acids, such as a mineral acid, e.g., dilute sulfuric acid. If a
hydration vessel is utilized, its contents are emptied into a
conversion vessel, e.g., a fermentation vessel, which includes one
or more conversion microbes, such as one or more yeasts, bacteria
or mixtures of yeasts and/or bacteria. If a hydration vessel is not
utilized, the milled material can be directly charged to the
conversion vessel, e.g., for fermentation.
After conversion, the remaining solids are removed and dried to
give distillers dry grains (DDG), while the ethanol is distilled
off. In some embodiments, a thermophilic microbe is utilized for
the conversion and the ethanol is continuously removed by
evaporation as it is produced. If desired, the distilled ethanol
can be fully dehydrated, such as by passing the wet ethanol through
a zeolite bed, or distilling with benzene.
Referring particularly now to FIG. 27, in some implementations, the
wet milling process for the conversion of corn kernels to anhydrous
ethanol begins with pretreating the dried corn kernels with any one
or more pretreatments described herein, such as radiation, e.g.,
any one or more types of radiation described herein (e.g., a beam
of electrons in which each electron has an energy of about 5 MeV).
After pre-treatment, the corn kernels are steeped in dilute
sulfuric acid and gently stirred to break the corn kernels into its
constituents. After steeping, the fiber, oil and germ portions are
fractionated and dried, and then combined with any solids remaining
after distillation to give corn gluten feed (CGF). After removing
germ and fiber, in some embodiments, the gluten is separated to
give corn gluten meal (CGM). The remaining starch can be pretreated
again (or for the first time) by any pretreatment described herein,
e.g., to reduce its molecular weight and/or to functionalize the
starch so that it is more soluble. In some embodiments, the starch
is then charged to a reaction vessel containing water and,
optionally, hydrating agents, such as surfactants. Optionally, this
reaction vessel can also include one or more enzymes, such as
amylase, to aid in further breakdown of starch, or the reaction
vessel may contain one or more acids, such as a mineral acid, e.g.,
dilute sulfuric acid. As shown, saccharification can occur in
several vessels and then the contents of the final vessel can be
emptied into a conversion vessel, e.g., a fermentation vessel,
which includes one or more conversion microbes, such as one or more
yeasts or bacteria.
After conversion, the ethanol is distilled off. In some
embodiments, a thermophilic microbe is utilized for the conversion
and the ethanol is continuously removed by evaporation as it is
produced. If desired, the distilled ethanol can be fully
dehydrated, such as by passing the wet ethanol through a zeolite
bed.
Gasification
In addition to using pyrolysis for pre-treatment of feedstock,
pyrolysis can also be used to process pre-treated feedstock to
extract useful materials. In particular, a form of pyrolysis known
as gasification can be employed to generate fuel gases along with
various other gaseous, liquid, and solid products. To perform
gasification, the pre-treated feedstock is introduced into a
pyrolysis chamber and heated to a high temperature, typically
700.degree. C. or more. The temperature used depends upon a number
of factors, including the nature of the feedstock and the desired
products.
Quantities of oxygen (e.g., as pure oxygen gas and/or as air) and
steam (e.g., superheated steam) are also added to the pyrolysis
chamber to facilitate gasification. These compounds react with
carbon-containing feedstock material in a multiple-step reaction to
generate a gas mixture called synthesis gas (or "syngas").
Essentially, during gasification, a limited amount of oxygen is
introduced into the pyrolysis chamber to allow some feedstock
material to combust to form carbon monoxide and generate process
heat. The process heat can then be used to promote a second
reaction that converts additional feedstock material to hydrogen
and carbon monoxide.
In a first step of the overall reaction, heating the feedstock
material produces a char that can include a wide variety of
different hydrocarbon-based species. Certain volatile materials can
be produced (e.g., certain gaseous hydrocarbon materials),
resulting in a reduction of the overall weight of the feedstock
material. Then, in a second step of the reaction, some of the
volatile material that is produced in the first step reacts with
oxygen in a combustion reaction to produce both carbon monoxide and
carbon dioxide. The combustion reaction releases heat, which
promotes the third step of the reaction. In the third step, carbon
dioxide and steam (e.g., water) react with the char generated in
the first step to form carbon monoxide and hydrogen gas. Carbon
monoxide can also react with steam, in a water gas shift reaction,
to form carbon dioxide and further hydrogen gas.
Gasification can be used as a primary process to generate products
directly from pre-treated feedstock for subsequent transport and/or
sale, for example. Alternatively, or in addition, gasification can
be used as an auxiliary process for generating fuel for an overall
processing system. The hydrogen-rich syngas that is generated via
the gasification process can be burned, for example, to generate
electricity and/or process heat that can be directed for use at
other locations in the processing system. As a result, the overall
processing system can be at least partially self-sustaining. A
number of other products, including pyrolysis oils and gaseous
hydrocarbon-based substances, can also be obtained during and/or
following gasification; these can be separated and stored or
transported as desired.
A variety of different pyrolysis chambers are suitable for
gasification of pre-treated feedstock, including the pyrolysis
chambers disclosed herein. In particular, fluidized bed reactor
systems, in which the pre-treated feedstock is fluidized in steam
and oxygen/air, provide relatively high throughput and
straightforward recovery of products. Solid char that remains
following gasification in a fluidized bed system (or in other
pyrolysis chambers) can be burned to generate additional process
heat to promote subsequent gasification reactions.
Syngas can be reformed using a Fischer-Tropsch process, which is a
catalyzed chemical reaction in which the synthesis gas is converted
into liquid alcohols and hydrocarbons. The most common catalysts
are based on iron and cobalt, although nickel and ruthenium have
also been used.
In an alternative process, a biofilm can be used to reform the
syngas to produce the liquid fuel instead of a chemical catalyst.
Such a process has been described by Coskata, Inc. Any of the
biomass materials described herein can be used in Coskata's
process.
In some embodiments, irradiating the biomass material, e.g., with a
beam of particles, such as electrons, prior to gasification can
lower the gasification temperature, resulting in less energy being
consumed during gasification, and can result in less char and tar
formation, resulting in enhanced syngas yield.
Post-Processing
Distillation
After fermentation, the resulting fluids can be distilled using,
for example, a "beer column" to separate ethanol and other alcohols
from the majority of water and residual solids. The vapor exiting
the beer column can be, e.g., 35% by weight ethanol, and can be fed
to a rectification column. A mixture of nearly azeotropic (92.5%)
ethanol and water from the rectification column can be purified to
pure (99.5%) ethanol using vapor-phase molecular sieves. The beer
column bottoms can be sent to the first effect of a three-effect
evaporator. The rectification column reflux condenser can provide
heat for this first effect. After the first effect, solids can be
separated using a centrifuge and dried in a rotary dryer. A portion
(25%) of the centrifuge effluent can be recycled to fermentation
and the rest sent to the second and third evaporator effects. Most
of the evaporator condensate can be returned to the process as
fairly clean condensate with a small portion split off to waste
water treatment to prevent build-up of low-boiling compounds.
Waste Water Treatment
Wastewater treatment is used to minimize makeup water requirements
of the plant by treating process water for reuse within the plant.
Wastewater treatment can also produce fuel (e.g., sludge and
biogas) that can be used to improve the overall efficiency of the
ethanol production process. For example, as described in further
detail below, sludge and biogas can be used to create steam and
electricity that can be used in various plant processes.
Wastewater is initially pumped through a screen (e.g., a bar
screen) to remove large particles, which are collected in a hopper.
In some embodiments, the large particles are sent to a landfill.
Additionally or alternatively, the large particles are burned to
create steam and/or electricity as described in further detail
below. In general, the spacing on the bar screen is between 1/4
inch to 1 inch spacing (e.g., 1/2 inch spacing).
The wastewater then flows to an equalization tank, where the
organic concentration of the wastewater is equalized during a
retention time. In general, the retention time is between 8 hours
and 36 hours (e.g., 24 hours). A mixer is disposed within the tank
to stir the contents of the tank. In some embodiments, mixers
disposed throughout the tank are used to stir the contents of the
tank. In certain embodiments, the mixer substantially mixes the
contents of the equalization tank such that conditions (e.g.,
wastewater concentration and temperature) throughout the tank are
uniform.
A first pump moves water from the equalization tank through a
liquid-to-liquid heat exchanger. The heat exchanger is controlled
(e.g., by controlling the flow rate of fluid through the heat
exchanger) such that wastewater exiting the heat exchanger is at a
desired temperature for anaerobic treatment. For example, the
desired temperature for anaerobic treatment can be between
40.degree. C. to 60.degree. C.
After exiting the heat exchanger, the wastewater enters one or more
anaerobic reactors. In some embodiments, the concentration of
sludge in each anaerobic reactor is the same as the overall
concentration of sludge in the wastewater. In other embodiments,
the anaerobic reactor has a higher concentration of sludge than the
overall concentration of sludge in the wastewater.
A nutrient solution containing nitrogen and phosphorus is metered
into each anaerobic reactor containing wastewater. The nutrient
solution reacts with the sludge in the anaerobic reactor to produce
biogas which can contain 50% methane and have a heating value of
approximately 12,000 British thermal units, or Btu, per pound). The
biogas exits each anaerobic reactor through a vent and flows into a
manifold, where several biogas streams are combined into a single
stream. A compressor moves the stream of biogas to a boiler or a
combustion engine as described in further detail below. In some
embodiments, the compressor also moves the single stream of biogas
through a desulphurization catalyst. Additionally or alternatively,
the compressor can move the single stream of biogas through a
sediment trap.
A second pump moves anaerobic effluent from the anaerobic reactors
to one or more aerobic reactors (e.g., activated sludge reactors).
An aerator is disposed within each aerobic reactor to mix the
anaerobic effluent, sludge, and oxygen (e.g., oxygen contained in
air). Within each aerobic reactor, oxidation of cellular material
in the anaerobic effluent produces carbon dioxide, water, and
ammonia.
Aerobic effluent moves (e.g., via gravity) to a separator, where
sludge is separated from treated water. Some of the sludge is
returned to the one or more aerobic reactors to create an elevated
sludge concentration in the aerobic reactors, thereby facilitating
the aerobic breakdown of cellular material in the wastewater. A
conveyor removes excess sludge from the separator. As described in
further detail below, the excess sludge is used as fuel to create
steam and/or electricity.
The treated water is pumped from the separator to a settling tank.
Solids dispersed throughout the treated water settle to the bottom
of the settling tank and are subsequently removed. After a settling
period, treated water is pumped from the settling tank through a
fine filter to remove any additional solids remaining in the water.
In some embodiments, chlorine is added to the treated water to kill
pathogenic bacteria. In some embodiments, one or more
physical-chemical separation techniques are used to further purify
the treated water. For example, treated water can be pumped through
a carbon adsorption reactor. As another example, treated water can
pumped through a reverse osmosis reactor.
In the processes disclosed herein, whenever water is used in any
process, it may be grey water, e.g., municipal grey water, or black
water. In some embodiments, the grey or black water is sterilized
prior to use. Sterilization may be accomplished by any desired
technique, for example by irradiation, steam, or chemical
sterilization.
Waste Combustion
The production of alcohol from biomass can result in the production
of various by-product streams useful for generating steam and
electricity to be used in other parts of the plant. For example,
steam generated from burning by-product streams can be used in the
distillation process. As another example, electricity generated
from burning by-product streams can be used to power electron beam
generators and ultrasonic transducers used in pretreatment.
The by-products used to generate steam and electricity are derived
from a number of sources throughout the process. For example,
anaerobic digestion of wastewater produces a biogas high in methane
and a small amount of waste biomass (sludge). As another example,
post-distillate solids (e.g., unconverted lignin, cellulose, and
hemicellulose remaining from the pretreatment and primary
processes) can be used as a fuel.
The biogas is diverted to a combustion engine connected to an
electric generator to produce electricity. For example, the biogas
can be used as a fuel source for a spark-ignited natural gas
engine. As another example, the biogas can be used as a fuel source
for a direct-injection natural gas engine. As another example, the
biogas can be used as a fuel source for a combustion turbine.
Additionally or alternatively, the combustion engine can be
configured in a cogeneration configuration. For example, waste heat
from the combustion engines can be used to provide hot water or
steam throughout the plant.
The sludge, and post-distillate solids are burned to heat water
flowing through a heat exchanger. In some embodiments, the water
flowing through the heat exchanger is evaporated and superheated to
steam. In certain embodiments, the steam is used in the
pretreatment rector and in heat exchange in the distillation and
evaporation processes. Additionally or alternatively, the steam
expands to power a multi-stage steam turbine connected to an
electric generator. Steam exiting the steam turbine is condensed
with cooling water and returned to the heat exchanger for reheating
to steam. In some embodiments, the flow rate of water through the
heat exchanger is controlled to obtain a target electricity output
from the steam turbine connected to an electric generator. For
example, water can be added to the heat exchanger to ensure that
the steam turbine is operating above a threshold condition (e.g.,
the turbine is spinning fast enough to turn the electric
generator).
While certain embodiments have been described, other embodiments
are possible.
As an example, while the biogas is described as being diverted to a
combustion engine connected to an electric generator, in certain
embodiments, the biogas can be passed through a fuel reformer to
produce hydrogen. The hydrogen is then converted to electricity
through a fuel cell.
As another example, while the biogas is described as being burned
apart from the sludge and post-distillate solids, in certain
embodiments, all of the waste by-products can be burned together to
produce steam.
Products/Co-Products
Alcohols
The alcohol produced can be a monohydroxy alcohol, e.g., ethanol,
or a polyhydroxy alcohol, e.g., ethylene glycol or glycerin.
Examples of alcohols that can be produced include methanol,
ethanol, propanol, isopropanol, butanol, e.g., n-, sec- or
t-butanol, ethylene glycol, propylene glycol, 1,4-butane diol,
glycerin or mixtures of these alcohols.
Each of the alcohols produced by the plant have commercial value as
industrial feedstock. For example, ethanol can be used in the
manufacture of varnishes and perfume. As another example, methanol
can be used as a solvent used as a component in windshield wiper
fluid. As still another example, butanol can be used in
plasticizers, resins, lacquers, and brake fluids.
Bioethanol produced by the plant is valuable as an ingredient used
in the food and beverage industry. For example, the ethanol
produced by the plant can be purified to food grade alcohol and
used as a primary ingredient in the alcoholic beverages.
Bioethanol produced by the plant also has commercial value as a
transportation fuel. The use of ethanol as a transportation fuel
can be implemented with relatively little capital investment from
spark ignition engine manufacturers and owners (e.g., changes to
injection timing, fuel-to-air ratio, and components of the fuel
injection system). Many automotive manufacturers currently offer
flex-fuel vehicles capable of operation on ethanol/gasoline blends
up to 85% ethanol by volume (e.g., standard equipment on a Chevy
Tahoe 4.times.4).
Bioethanol produced by this plant can be used as an engine fuel to
improve environmental and economic conditions beyond the location
of the plant. For example, ethanol produced by this plant and used
as a fuel can reduce greenhouse gas emissions from manmade sources
(e.g., transportation sources). As another example, ethanol
produced by this plant and used as an engine fuel can also displace
consumption of gasoline refined from oil.
Bioethanol has a greater octane number than conventional gasoline
and, thus, can be used to improve the performance (e.g., allow for
higher compression ratios) of spark ignition engines. For example,
small amounts (e.g., 10% by volume) of ethanol can be blended with
gasoline to act as an octane enhancer for fuels used in spark
ignition engines. As another example, larger amounts (e.g., 85% by
volume) of ethanol can be blended with gasoline to further increase
the fuel octane number and displace larger volumes of gasoline.
Bioethanol strategies are discussed, e.g., by DiPardo in Journal of
Outlook for Biomass Ethanol Production and Demand (EIA Forecasts),
2002; Sheehan in Biotechnology Progress, 15:8179, 1999; Martin in
Enzyme Microbes Technology, 31:274, 2002; Greer in BioCycle, 61-65,
April 2005; Lynd in Microbiology and Molecular Biology Reviews,
66:3, 506-577, 2002; Ljungdahl et al., in U.S. Pat. No. 4,292,406;
and Bellamy, in U.S. Pat. No. 4,094,742.
Organic Acids
The organic acids produced can include monocarboxylic acids or
polycarboxylic acids. Examples of organic acids include formic
acid, acetic acid, propionic acid, butyric acid, valeric acid,
caproic, palmitic acid, stearic acid, oxalic acid, malonic acid,
succinic acid, glutaric acid, oleic acid, linoleic acid, glycolic
acid, lactic acid, .gamma.-hydroxybutyric acid or mixtures of these
acids.
Co-Products
Lignin Residue
As described above, lignin-containing residues from primary and
pretreatment processes has value as a high/medium energy fuel and
can be used to generate power and steam for use in plant processes.
However, such lignin residues are a new type of solids fuel and
there is little demand for it outside of the plant boundaries, and
the costs of drying it for transportation only subtract from its
potential value. In some cases, gasification of the lignin residues
can convert it to a higher-value product with lower Cost.
Other Co-Products
Cell matter, furfural, and acetic acid have been identified as
potential co-products of biomass-to-fuel processing facilities.
Interstitial cell matter could be valuable, but might require
significant purification. Markets for furfural and acetic acid are
in place, although it is unlikely that they are large enough to
consume the output of a fully commercialized
lignocellulose-to-ethanol industry.
EXAMPLES
The following Examples are intended to illustrate, and do not limit
the teachings of this disclosure.
Example 1
Preparation of Fibrous Material from Polycoated Paper
A 1500 pound skid of virgin, half-gallon juice cartons made of
un-printed polycoated white Kraft board having a bulk density of 20
lb/ft.sup.3 was obtained from International Paper. Each carton was
folded flat, and then fed into a 3 hp Flinch Baugh shredder at a
rate of approximately 15 to 20 pounds per hour. The shredder was
equipped with two 12 inch rotary blades, two fixed blades and a
0.30 inch discharge screen. The gap between the rotary and fixed
blades was adjusted to 0.10 inch. The output from the shredder
resembled confetti having a width of between 0.1 inch and 0.5 inch,
a length of between 0.25 inch and 1 inch and a thickness equivalent
to that of the starting material (about 0.075 inch).
The confetti-like material was fed to a Munson rotary knife cutter,
Model SC30. Model SC30 is equipped with four rotary blades, four
fixed blades, and a discharge screen having 1/8 inch openings. The
gap between the rotary and fixed blades was set to approximately
0.020 inch. The rotary knife cutter sheared the confetti-like
pieces across the knife-edges, tearing the pieces apart and
releasing a fibrous material at a rate of about one pound per hour.
The fibrous material had a BET surface area of 0.9748
m.sup.2/g+/-0.0167 m.sup.2/g, a porosity of 89.0437 percent and a
bulk density (@0.53 psia) of 0.1260 g/mL. An average length of the
fibers was 1.141 mm and an average width of the fibers was 0.027
mm, giving an average L/D of 42:1. A scanning electron micrograph
of the fibrous material is shown in FIG. 28 at 25.times.
magnification.
Example 2
Preparation of Fibrous Material from Bleached Kraft Board
A 1500 pound skid of virgin bleached white Kraft board having a
bulk density of 30 lb/ft.sup.3 was obtained from International
Paper. The material was folded flat, and then fed into a 3 hp
Flinch Baugh shredder at a rate of approximately 15 to 20 pounds
per hour. The shredder was equipped with two 12 inch rotary blades,
two fixed blades and a 0.30 inch discharge screen. The gap between
the rotary and fixed blades was adjusted to 0.10 inch. The output
from the shredder resembled confetti having a width of between 0.1
inch and 0.5 inch, a length of between 0.25 inch and 1 inch and a
thickness equivalent to that of the starting material (about 0.075
inch). The confetti-like material was fed to a Munson rotary knife
cutter, Model SC30. The discharge screen had 1/8 inch openings. The
gap between the rotary and fixed blades was set to approximately
0.020 inch. The rotary knife cutter sheared the confetti-like
pieces, releasing a fibrous material at a rate of about one pound
per hour. The fibrous material had a BET surface area of 1.1316
m.sup.2/g+/-0.0103 m.sup.2/g, a porosity of 88.3285 percent and a
bulk density (@0.53 psia) of 0.1497 g/mL. An average length of the
fibers was 1.063 mm and an average width of the fibers was 0.0245
mm, giving an average L/D of 43:1. A scanning electron micrograph
of the fibrous material is shown in FIG. 29 at 25.times.
magnification.
Example 3
Preparation of Twice Sheared Fibrous Material from Bleached Kraft
Board
A 1500 pound skid of virgin bleached white Kraft board having a
bulk density of 30 lb/ft.sup.3 was obtained from International
Paper. The material was folded flat, and then fed into a 3 hp
Flinch Baugh shredder at a rate of approximately 15 to 20 pounds
per hour. The shredder was equipped with two 12 inch rotary blades,
two fixed blades and a 0.30 inch discharge screen. The gap between
the rotary and fixed blades was adjusted to 0.10 inch. The output
from the shredder resembled confetti (as above). The confetti-like
material was fed to a Munson rotary knife cutter, Model SC30. The
discharge screen had 1/16 inch openings. The gap between the rotary
and fixed blades was set to approximately 0.020 inch. The rotary
knife cutter the confetti-like pieces, releasing a fibrous material
at a rate of about one pound per hour. The material resulting from
the first shearing was fed back into the same setup described above
and sheared again. The resulting fibrous material had a BET surface
area of 1.4408 m.sup.2/g+/-0.0156 m.sup.2/g, a porosity of 90.8998
percent and a bulk density (@0.53 psia) of 0.1298 g/mL. An average
length of the fibers was 0.891 mm and an average width of the
fibers was 0.026 mm, giving an average LID of 34:1. A scanning
electron micrograph of the fibrous material is shown in FIG. 30 at
25.times. magnification.
Example 4
Preparation of Thrice Sheared Fibrous Material from Bleached Kraft
Board
A 1500 pound skid of virgin bleached white Kraft board having a
bulk density of 30 lb/ft.sup.3 was obtained from International
Paper. The material was folded flat, and then fed into a 3 hp
Flinch Baugh shredder at a rate of approximately 15 to 20 pounds
per hour. The shredder was equipped with two 12 inch rotary blades,
two fixed blades and a 0.30 inch discharge screen. The gap between
the rotary and fixed blades was adjusted to 0.10 inch. The output
from the shredder resembled confetti (as above). The confetti-like
material was fed to a Munson rotary knife cutter, Model SC30. The
discharge screen had 1/8 inch openings. The gap between the rotary
and fixed blades was set to approximately 0.020 inch. The rotary
knife cutter sheared the confetti-like pieces across the
knife-edges. The material resulting from the first shearing was fed
back into the same setup and the screen was replaced with a 1/16
inch screen. This material was sheared. The material resulting from
the second shearing was fed back into the same setup and the screen
was replaced with a 1/32 inch screen. This material was sheared.
The resulting fibrous material had a BET surface area of 1.6897
m.sup.2/g+/-0.0155 m.sup.2/g, a porosity of 87.7163 percent and a
bulk density (@0.53 psia) of 0.1448 g/mL. An average length of the
fibers was 0.824 mm and an average width of the fibers was 0.0262
mm, giving an average L/D of 32:1. A scanning electron micrograph
of the fibrous material is shown in FIG. 31 at 25.times.
magnification.
Example 5
Preparation of Densified Fibrous Material from Bleached Kraft Board
Without Added Binder
Fibrous material was prepared according to Example 2. Approximately
1 lb of water was sprayed onto each 10 lb of fibrous material. The
fibrous material was densified using a California Pellet Mill 1100
operating at 75.degree. C. Pellets were obtained having a bulk
density ranging from about 7 lb/ft.sup.3 to about 15
lb/ft.sup.3.
Example 6
Preparation of Densified Fibrous Material from Bleached Kraft Board
with Binder
Fibrous material was prepared according to Example 2.
A 2 weight percent stock solution of POLYOX.TM. WSR N10
(polyethylene oxide) was prepared in water.
Approximately 1 lb of the stock solution was sprayed onto each 10
lb of fibrous material. The fibrous material was densified using a
California Pellet Mill 1100 operating at 75.degree. C. Pellets were
obtained having a bulk density ranging from about 15 lb/ft.sup.3 to
about 40 lb/ft.sup.3.
Example 7
Reducing the Molecular Weight of Cellulose in Fibrous Kraft Paper
by Gamma Radiation with Minimum Oxidation
Fibrous material is prepared according to Example 4. The fibrous
Kraft paper is densified according to Example 5.
The densified pellets are placed in a glass ampoule having a
maximum capacity of 250 mL. The glass ampoule is evacuated under
high vacuum (10.sup.-5 torr) for 30 minutes, and then back-filled
with argon gas. The ampoule is sealed under argon. The pellets in
the ampoule are irradiated with gamma radiation for about 3 hours
at a dose rate of about 1 Mrad per hour to provide an irradiated
material in which the cellulose has a lower molecular weight than
the fibrous Kraft starting material.
Example 8
Reducing the Molecular Weight of Cellulose in Fibrous Kraft Paper
by Gamma Radiation with Maximum Oxidation
Fibrous material is prepared according to Example 4. The fibrous
Kraft paper is densified according to Example 5.
The densified pellets are placed in a glass ampoule having a
maximum capacity of 250 mL. The glass ampoule is sealed under an
atmosphere of air. The pellets in the ampoule are irradiated with
gamma radiation for about 3 hours at a dose rate of about 1 Mrad
per hour to provide an irradiated material in which the cellulose
has a lower molecular weight than the fibrous Kraft starting
material.
Example 9
Methods of Determining Molecular Weight of Cellulosic and
Lignocellulosic Materials by Gel Permeation Chromatography
Cellulosic and lignocellulosic materials for analysis were treated
according to Example 4. Sample materials presented in the following
tables include Kraft paper (P), wheat straw (WS), alfalfa (A), and
switchgrass (SG). The number "132" of the Sample ID refers to the
particle size of the material after shearing through a 1/32 inch
screen. The number after the dash refers to the dosage of radiation
(MRad) and "US" refers to ultrasonic treatment. For example, a
sample ID "P132-10" refers to Kraft paper that has been sheared to
a particle size of 132 mesh and has been irradiated with 10
MRad.
TABLE-US-00003 TABLE 1 Peak Average Molecular Weight of Irradiated
Kraft Paper Sample Dosage.sup.1 Average MW .+-. Source Sample ID
(MRad) Ultrasound.sup.2 Std Dev. Kraft Paper P132 0 No 32853 .+-.
10006 P132-10 10 '' 61398 .+-. 2468** P132-100 100 '' 8444 .+-. 580
P132-181 181 '' 6668 .+-. 77 P132-US 0 Yes 3095 .+-. 1013 **Low
doses of radiation appear to increase the molecular weight of some
materials .sup.1Dosage Rate = 1 MRad/hour .sup.2Treatment for 30
minutes with 20 kHz ultrasound using a 1000 W horn under
re-circulating conditions with the material dispersed in water.
TABLE-US-00004 TABLE 2 Peak Average Molecular Weight of Irradiated
Materials Dosage.sup.1 Average MW .+-. Sample ID Peak # (MRad)
Ultrasound.sup.2 Std Dev. WS132 1 0 No 1407411 .+-. 175191 2 '' ''
39145 .+-. 3425 3 '' '' 2886 .+-. 177 WS132-10* 1 10 '' 26040 .+-.
3240 WS132-100* 1 100 '' 23620 .+-. 453 A132 1 0 '' 1604886 .+-.
151701 2 '' '' 37525 .+-. 3751 3 '' '' 2853 .+-. 490 A132-10* 1 10
'' 50853 .+-. 1665 2 '' '' 2461 .+-. 17 A132-100* 1 100 '' 38291
.+-. 2235 2 '' '' 2487 .+-. 15 SG132 1 0 '' 1557360 .+-. 83693 2 ''
'' 42594 .+-. 4414 3 '' '' 3268 .+-. 249 SG132-10* 1 10 '' 60888
.+-. 9131 SG132-100* 1 100 '' 22345 .+-. 3797 SG132-10-US 1 10 Yes
86086 .+-. 43518 2 '' '' 2247 .+-. 468 SG132-100-US 1 100 '' 4696
.+-. 1465 *Peaks coalesce after treatment **Low doses of radiation
appear to increase the molecular weight of some materials
.sup.1Dosage Rate = 1 MRad/hour .sup.2Treatment for 30 minutes with
20 kHz ultrasound using a 1000 W horn under re-circulating
conditions with the material dispersed in water.
Gel Permeation Chromatography (GPC) is used to determine the
molecular weight distribution of polymers. During GPC analysis, a
solution of the polymer sample is passed through a column packed
with a porous gel trapping small molecules. The sample is separated
based on molecular size with larger molecules eluting sooner than
smaller molecules. The retention time of each component is most
often detected by refractive index (RI), evaporative light
scattering (ELS), or ultraviolet (UV) and compared to a calibration
curve. The resulting data is then used to calculate the molecular
weight distribution for the sample.
A distribution of molecular weights rather than a unique molecular
weight is used to characterize synthetic polymers. To characterize
this distribution, statistical averages are utilized. The most
common of these averages are the "number average molecular weight"
(M.sub.n) and the "weight average molecular weight" (M.sub.w).
Methods of calculating these values are described in the art, e.g.,
in Example 9 of WO 2008/073186.
The polydispersity index or PI is defined as the ratio of
M.sub.w/M.sub.n. The larger the PI, the broader or more disperse
the distribution. The lowest value that a PI can be is 1. This
represents a monodisperse sample; that is, a polymer with all of
the molecules in the distribution being the same molecular
weight.
The peak molecular weight value (M.sub.P) is another descriptor
defined as the mode of the molecular weight distribution. It
signifies the molecular weight that is most abundant in the
distribution. This value also gives insight to the molecular weight
distribution.
Most GPC measurements are made relative to a different polymer
standard. The accuracy of the results depends on how closely the
characteristics of the polymer being analyzed match those of the
standard used. The expected error in reproducibility between
different series of determinations, calibrated separately, is ca.
5-10% and is characteristic to the limited precision of GPC
determinations. Therefore, GPC results are most useful when a
comparison between the molecular weight distributions of different
samples is made during the same series of determinations.
The lignocellulosic samples required sample preparation prior to
GPC analysis. First, a saturated solution (8.4% by weight) of
lithium chloride (LiCl) was prepared in dimethyl acetamide (DMAc).
Approximately 100 mg of each sample was added to approximately 10 g
of a freshly prepared saturated LiCl/DMAc solution, and each
mixture was heated to approximately 150.degree. C.-170.degree. C.
with stirring for 1 hour. The resulting solutions were generally
light- to dark-yellow in color. The temperature of the solutions
was decreased to approximately 100.degree. C. and the solutions
were heated for an additional 2 hours. The temperature of the
solutions was then decreased to approximately 50.degree. C. and
each sample solution was heated for approximately 48 to 60 hours.
Of note, samples irradiated at 100 MRad were more easily
solubilized as compared to their untreated counterpart.
Additionally, the sheared samples (denoted by the number 132) had
slightly lower average molecular weights as compared with uncut
samples.
The resulting sample solutions were diluted 1:1 using DMAc as
solvent and were filtered through a 0.45 .mu.m PTFE filter. The
filtered sample solutions were then analyzed by GPC. The peak
average molecular weight (Mp) of the samples, as determined by Gel
Permeation Chromatography (GPC), are summarized in Tables 1 and 2.
Each sample was prepared in duplicate and each preparation of the
sample was analyzed in duplicate (two injections) for a total of
four injections per sample. The EasiCal polystyrene standards PS1A
and PS1B were used to generate a calibration curve for the
molecular weight scale from about 580 to 7,500,00 Daltons.
TABLE-US-00005 TABLE 3 GPC Analysis Conditions Instrument: Waters
Alliance GPC 2000 Plgel 10.mu. Mixed-B Columns (3): S/N's:
10M-MB-148-83; 10M-MB-148-84; 10M-MB-174-129 Mobile Phase
(solvent): 0.5% LiCl in DMAc (1.0 mL/min.) Column/Detector
Temperature: 70.degree. C. Injector Temperature: 70.degree. C.
Sample Loop Size: 323.5 .mu.L
Example 10
Determining Crystallinity of Irradiated Material by X-Ray
Diffraction
X-ray diffraction (XRD) is a method by which a crystalline sample
is irradiated with monoenergetic x-rays. The interaction of the
lattice structure of the sample with these x-rays is recorded and
provides information about the crystalline structure being
irradiated. The resulting characteristic "fingerprint" allows for
the identification of the crystalline compounds present in the
sample. Using a whole-pattern fitting analysis (the Rietvelt
Refinement), it is possible to perform quantitative analyses on
samples containing more than one crystalline compound.
TABLE-US-00006 TABLE 4 XRD Data Including Domain Size and %
Crystallinity Domain Size Sample ID (.ANG.) % Crystallinity P132 55
55 P132-10 46 58 P132-100 50 55 P132-181 48 52 P132-US 26 40 A132
28 42 A132-10 26 40 A132-100 28 35 WS132 30 36 WS132-10 27 37
WS132-100 30 41 SG132 29 40 SG132-10 28 38 SG132-100 28 37
SG132-10-US 25 42 SG132-100-US 21 34
Each sample was placed on a zero background holder and placed in a
Phillips PW1800 diffractometer using Cu radiation. Scans were then
run over the range of 5.degree. to 50.degree. with a step size of
0.05.degree. and a counting time of 2 hours each.
Once the diffraction patterns were obtained, the phases were
identified with the aid of the Powder Diffraction File published by
the International Centre for Diffraction Data. In all samples the
crystalline phase identified was cellulose--Ia, which has a
triclinic structure.
The distinguishing feature among the 20 samples is the peak
breadth, which is related to the crystallite domain size. The
experimental peak breadth was used to compute the domain size and
percent crystallinity, which are reported in Table 4.
Percent crystallinity (X.sub.c %) is measured as a ratio of the
crystalline area to the total area under the x-ray diffraction
peaks,
.times..times..times..times. ##EQU00006## where, A.sub.c=Area of
crystalline phase A.sub.a=Area of amorphous phase X.sub.c=Percent
of crystallinity
To determine the percent crystallinity for each sample it was
necessary to first extract the amount of the amorphous phase. This
is done by estimating the area of each diffraction pattern that can
be attributed to the crystalline phase (represented by the sharper
peaks) and the non-crystalline phase (represented by the broad
humps beneath the pattern and centered at 22.degree. and
38.degree..
A systematic process was used to minimize error in these
calculations due to broad crystalline peaks as well as high
background intensity. First, a linear background was applied and
then removed. Second, two Gaussian peaks centered at 22.degree. and
38.degree. with widths of 10-12.degree. each were fitted to the
humps beneath the crystalline peaks. Third, the area beneath the
two broad Gaussian peaks and the rest of the pattern were
determined. Finally, percent crystallinity was calculated by
dividing the area beneath the crystalline peak by the total
intensity (after background subtraction). Domain size and %
crystallinity of the samples as determined by X-ray diffraction
(XRD) are presented in Table 4.
Example 11
Porosimetry Analysis of Irradiated Materials
Mercury pore size and pore volume analysis (Table 5) is based on
forcing mercury (a non-wetting liquid) into a porous structure
under tightly controlled pressures. Since mercury does not wet most
substances and will not spontaneously penetrate pores by capillary
action, it must be forced into the voids of the sample by applying
external pressure. The pressure required to fill the voids is
inversely proportional to the size of the pores. Only a small
amount of force or pressure is required to fill large voids,
whereas much greater pressure is required to fill voids of very
small pores.
TABLE-US-00007 TABLE 5 Pore Size and Volume Distribution by Mercury
Porosimetry Median Median Average Bulk Total Total Pore Pore Pore
Density Apparent Intrusion Pore Diameter Diameter Diameter @ 0.50
(skeletal) Volume Area (Volume) (Area) (4 V/A) psia Density
Porosity Sample ID (mL/g) (m.sup.2/g) (.mu.m) (.mu.m) (.mu.m)
(g/mL) (g/mL) (%) P132 6.0594 1.228 36.2250 13.7278 19.7415 0.1448
1.1785 87.7163 P132-10 5.5436 1.211 46.3463 4.5646 18.3106 0.1614
1.5355 89.4875 P132-100 5.3985 0.998 34.5235 18.2005 21.6422 0.1612
1.2413 87.0151 P132-181 3.2866 0.868 25.3448 12.2410 15.1509 0.2497
1.3916 82.0577 P132-US 6.0005 14.787 98.3459 0.0055 1.6231 0.1404
0.8894 84.2199 A132 2.0037 11.759 64.6308 0.0113 0.6816 0.3683
1.4058 73.7990 A132-10 1.9514 10.326 53.2706 0.0105 0.7560 0.3768
1.4231 73.5241 A132-100 1.9394 10.205 43.8966 0.0118 0.7602 0.3760
1.3889 72.9264 SG132 2.5267 8.265 57.6958 0.0141 1.2229 0.3119
1.4708 78.7961 SG132-10 2.1414 8.643 26.4666 0.0103 0.9910 0.3457
1.3315 74.0340 SG132-100 2.5142 10.766 32.7118 0.0098 0.9342 0.3077
1.3590 77.3593 SG132-10-US 4.4043 1.722 71.5734 1.1016 10.2319
0.1930 1.2883 85.0169 SG132-100-US 4.9665 7.358 24.8462 0.0089
2.6998 0.1695 1.0731 84.2010 WS132 2.9920 5.447 76.3675 0.0516
2.1971 0.2773 1.6279 82.9664 WS132-10 3.1138 2.901 57.4727 0.3630
4.2940 0.2763 1.9808 86.0484 WS132-100 3.2077 3.114 52.3284 0.2876
4.1199 0.2599 1.5611 83.3538
The AutoPore 9520 can attain a maximum pressure of 414 MPa or
60,000 psia. There are four low-pressure stations for sample
preparation and collection of macropore data from 0.2 psia to 50
psia. There are two high-pressure chambers, which collect data from
25 psia to 60,000 psia. The sample is placed in a bowl-like
apparatus called a penetrometer, which is bonded to a glass
capillary stem with a metal coating. As mercury invades the voids
in and around the sample, it moves down the capillary stem. The
loss of mercury from the capillary stem results in a change in the
electrical capacitance. The change in capacitance during the
experiment is converted to volume of mercury by knowing the stem
volume of the penetrometer in use. A variety of penetrometers with
different bowl (sample) sizes and capillaries are available to
accommodate most sample sizes and configurations. Table 6 below
defines some of the key parameters calculated for each sample.
TABLE-US-00008 TABLE 6 Definition of Parameters Parameter
Description Total Intrusion Volume: The total volume of mercury
intruded during an experiment. This can include interstitial
filling between small particles, porosity of sample, and
compression volume of sample. Total Pore Area: The total intrusion
volume converted to an area assuming cylindrical shaped pores.
Median Pore Diameter The size at the 50.sup.th percentile on the
cumulative volume graph. (volume): Median Pore Diameter (area): The
size at the 50.sup.th percentile on the cumulative area graph.
Average Pore Diameter: The total pore volume divided by the total
pore area (4V/A). Bulk Density: The mass of the sample divided by
the bulk volume. Bulk volume is determined at the filling pressure,
typically 0.5 psia. Apparent Density: The mass of sample divided by
the volume of sample measured at highest pressure, typically 60,000
psia. Porosity: (Bulk Density/Apparent Density) .times. 100%
Example 12
Particle Size Analysis of Irradiated Materials
The technique of particle sizing by static light scattering is
based on Mie theory (which also encompasses Fraunhofer theory). Mie
theory predicts the intensity vs. angle relationship as a function
of the size for spherical scattering particles provided that other
system variables are known and held constant. These variables are
the wavelength of incident light and the relative refractive index
of the sample material. Application of Mie theory provides the
detailed particle size information. Table 7 summarizes particle
size using median diameter, mean diameter, and modal diameter as
parameters.
TABLE-US-00009 TABLE 7 Particle Size by Laser Light Scattering (Dry
Sample Dispersion) Median Diameter Mean Diameter Modal Diameter
Sample ID (.mu.m) (.mu.m) (.mu.m) A132 380.695 418.778 442.258
A132-10 321.742 366.231 410.156 A132-100 301.786 348.633 444.169
SG132 369.400 411.790 455.508 SG132-10 278.793 325.497 426.717
SG132-100 242.757 298.686 390.097 WS132 407.335 445.618 467.978
WS132-10 194.237 226.604 297.941 WS132-100 201.975 236.037
307.304
Particle size was determined by Laser Light Scattering (Dry Sample
Dispersion) using a Malvern Mastersizer 2000 using the following
conditions:
TABLE-US-00010 Feed Rate: 35% Disperser Pressure: 4 Bar Optical
Model: (2.610, 1.000i), 1.000
An appropriate amount of sample was introduced onto a vibratory
tray. The feed rate and air pressure were adjusted to ensure that
the particles were properly dispersed. The key component is
selecting an air pressure that will break up agglomerations, but
does not compromise the sample integrity. The amount of sample
needed varies depending on the size of the particles. In general,
samples with fine particles require less material than samples with
coarse particles.
Example 13
Surface Area Analysis of Irradiated Materials
TABLE-US-00011 TABLE 8 Summary of Surface Area by Gas Adsorption
Surface area of each sample was analyzed using a Micromeritics ASAP
2420 Accelerated Surface Area and Porosimetry System. The samples
were prepared by first degassing for 16 hours at 40.degree. C.
Next, free space (both warm and cold) with helium is calculated and
then the sample tube is evacuated again to remove the helium. Data
collection begins after this second evacuation and consists of
defining target pressures, which controls how much gas is dosed
onto the sample. At each target pressure, the quantity of gas
adsorbed and the actual pressure are determined and recorded. The
pressure inside the sample tube is measured with a pressure
transducer. Additional doses of gas will continue until the target
pressure is achieved and allowed to equilibrate. The quantity of
gas adsorbed is determined by summing multiple doses onto the
sample. The pressure and quantity define a gas adsorption isotherm
and are used to calculate a including BET surface area (Table 8).
BET Surface Sample ID Single point surface area (m.sup.2/g) Area
(m.sup.2/g) P132 @ P/Po = 0.250387771 1.5253 1.6897 P132-10 @ P/Po
= 0.239496722 1.0212 1.2782 P132-100 @ P/Po = 0.240538100 1.0338
1.2622 P132-181 @ P/Po = 0.239166091 0.5102 0.6448 P132-US @ P/Po =
0.217359072 1.0983 1.6793 A132 @ P/Po = 0.240040610 0.5400 0.7614
A132-10 @ P/Po = 0.211218936 0.5383 0.7212 A132-100 @ P/Po =
0.238791097 0.4258 0.5538 SG132 @ P/Po = 0.237989353 0.6359 0.8350
SG132-10 @ P/Po = 0.238576905 0.6794 0.8689 SG132-100 @ P/Po =
0.241960361 0.5518 0.7034 SG132-10-US @ P/Po = 0.225692889 0.5693
0.7510 SG132-100-US @ P/Po = 0.225935246 1.0983 1.4963 WS132 @ P/Po
= 0.237823664 0.6582 0.8663 WS132-10 @ P/Po = 0.238612476 0.6191
0.7912 WS132-100 @ P/Po = 0.238398832 0.6255 0.8143
The BET model for isotherms is a widely used theory for calculating
the specific surface area. The analysis involves determining the
monolayer capacity of the sample surface by calculating the amount
required to cover the entire surface with a single densely packed
layer of krypton. The monolayer capacity is multiplied by the cross
sectional area of a molecule of probe gas to determine the total
surface area. Specific surface area is the surface area of the
sample aliquot divided by the mass of the sample.
Example 14
Fiber Length Determination of Irradiated Materials
Fiber length distribution testing was performed in triplicate on
the samples submitted using the Techpap MorFi LB01 system. The
average length and width are reported in Table 9.
TABLE-US-00012 TABLE 9 Summary of Lignocellulosic Fiber Length and
Width Data Statistically Corrected Average Average Arithmetic
Length Length Width Average Weighted in Weighted in (micrometers)
Sample ID (mm) Length (mm) Length (mm) (.mu.m) P132-10 0.484 0.615
0.773 24.7 P132-100 0.369 0.423 0.496 23.8 P132-181 0.312 0.342
0.392 24.4 A132-10 0.382 0.423 0.650 43.2 A132-100 0.362 0.435
0.592 29.9 SG132-10 0.328 0.363 0.521 44.0 SG132-100 0.325 0.351
0.466 43.8 WS132-10 0.353 0.381 0.565 44.7 WS132-100 0.354 0.371
0.536 45.4
Example 15
Ultrasonic Treatment of Irradiated and Un-Irradiated
Switchgrass
Switchgrass was sheared according to Example 4. The switchgrass was
treated by ultrasound alone or irradiation with 10 Mrad or 100 Mrad
of gamma rays, and then sonicated. The resulting materials
correspond to G132-BR (un-irradiated), G132-10-BR (10 Mrad and
sonication) and G132-100-BR (100 Mrad and sonication), as presented
in Table 1. Sonication was performed on each sample for 30 minutes
using 20 kHz ultrasound from a 1000 W horn under re-circulating
conditions. Each sample was dispersed in water at a concentration
of about 0.10 g/mL.
FIGS. 32 and 33 show the apparatus used for sonication. Apparatus
500 includes a converter 502 connected to booster 504 communicating
with a horn 506 fabricated from titanium or an alloy of titanium.
The horn, which has a seal 510 made from VITON.RTM. about its
perimeter on its processing side, forms a liquid tight seal with a
processing cell 508. The processing side of the horn is immersed in
a liquid, such as water, that has dispersed therein the sample to
be sonicated. Pressure in the cell is monitored with a pressure
gauge 512. In operation, each sample is moved by pump 517 from tank
516 through the processing cell and is sonicated. After,
sonication, the sample is captured in tank 520. The process can be
reversed in that the contents of tank 520 can be sent through the
processing cell and captured in tank 516. This process can be
repeated a number of times until a desired level of processing is
delivered to the sample.
Example 16
Scanning Electron Micrographs of Un-Irradiated Switchgrass in
Comparison to Irradiated and Irradiated and Sonicated
Switchgrass
Switchgrass samples for the scanning electron micrographs were
applied to carbon tape and gold sputter coated (70 seconds). Images
were taken with a JEOL 6500 field emission scanning electron
microscope.
FIG. 34 is a scanning electron micrograph at 1000.times.
magnification of a fibrous material produced from shearing
switchgrass on a rotary knife cutter, and then passing the sheared
material through a 1/32 inch screen.
FIGS. 35 and 36 are scanning electron micrographs of the fibrous
material of FIG. 34 after irradiation with 10 Mrad and 100 Mrad
gamma rays, respectively, at 1000.times. magnification.
FIG. 37 is a scanning electron micrographs of the fibrous material
of FIG. 34 after irradiation with 10 Mrad and sonication at
1000.times. magnification.
FIG. 38 is a scanning electron micrographs of the fibrous material
of FIG. 34 after irradiation with 100 Mrad and sonication at
1000.times. magnification.
Example 17
Infrared Spectrum of Irradiated Kraft Paper in Comparison to
Un-irradiated Kraft Paper
The FT-IR analysis was performed on a Nicolet/Impact 400. The
results indicate that all samples reported in Table 1 are
consistent with a cellulose-based material.
FIG. 39 is an infrared spectrum of Kraft board paper sheared
according to Example 4, while FIG. 40 is an infrared spectrum of
the Kraft paper of FIG. 39 after irradiation with 100 Mrad of gamma
radiation. The irradiated sample shows an additional peak in region
A (centered about 1730 cm.sup.-1) that is not found in the
un-irradiated material.
Example 18
Combination of Electron Beam and Sonication Pretreatment
Switchgrass is used as the feedstock and is sheared with a Munson
rotary knife cutter into a fibrous material. The fibrous material
is then evenly distributed onto an open tray composed of tin with
an area of greater than about 500 in.sup.2. The fibrous material is
distributed so that it has a depth of about 1-2 inches in the open
tray. The fibrous material may be distributed in plastic bags at
lower doses of irradiation (under 10 MRad), and left uncovered on
the metal tray at higher doses of radiation.
Separate samples of the fibrous material are then exposed to
successive doses of electron beam radiation to achieve a total dose
of 1 Mrad, 2 Mrad, 3, Mrad, 5 Mrad, 10 Mrad, 50 Mrad, and 100 Mrad.
Some samples are maintained under the same conditions as the
remaining samples, but are not irradiated, to serve as controls.
After cooling, the irradiated fibrous material is sent on for
further processing through a sonication device.
The sonication device includes a converter connected to booster
communicating with a horn fabricated from titanium or an alloy of
titanium. The horn, which has a seal made from VITON.RTM. about its
perimeter on its processing side, forms a liquid tight seal with a
processing cell. The processing side of the horn is immersed in a
liquid, such as water, into which the irradiated fibrous material
to be sonicated is immersed. Pressure in the cell is monitored with
a pressure gauge. In operation, each sample is moved by pump
through the processing cell and is sonicated.
To prepare the irradiated fibrous material for sonication, the
irradiated fibrous material is removed from any container (e.g.,
plastic bags) and is dispersed in water at a concentration of about
0.10 g/mL. Sonication is performed on each sample for 30 minutes
using 20 kHz ultrasound from a 1000 W horn under re-circulating
conditions. After sonication, the irradiated fibrous material is
captured in a tank. This process can be repeated a number of times
until a desired level of processing is achieved based on monitoring
the structural changes in the switchgrass. Again, some irradiated
samples are kept under the same conditions as the remaining
samples, but are not sonicated, to serve as controls. In addition,
some samples that were not irradiated are sonicated, again to serve
as controls. Thus, some controls are not processed, some are only
irradiated, and some are only sonicated.
Example 19
Microbial Testing of Pretreated Biomass
Specific lignocellulosic materials pretreated as described herein
are analyzed for toxicity to common strains of yeast and bacteria
used in the biofuel industry for the fermentation step in ethanol
production. Additionally, sugar content and compatibility with
cellulase enzymes are examined to determine the viability of the
treatment process. Testing of the pretreated materials is carried
out in two phases as follows.
I. Toxicity and Sugar Content
Toxicity of the pretreated grasses and paper feedstocks is measured
in yeast Saccharomyces cerevisiae (wine yeast) and Pichia stipitis
(ATCC 66278) as well as the bacteria Zymomonas mobilis (ATCC 31821)
and Clostridium thermocellum (ATCC 31924). A growth study is
performed with each of the organisms to determine the optimal time
of incubation and sampling.
Each of the feedstocks is then incubated, in duplicate, with S.
cerevisiae, P. stipitis, Z. mobilis, and C. thermocellum in a
standard microbiological medium for each organism. YM broth is used
for the two yeast strains, S. cerevisiae and P. stipitis. RM medium
is used for Z. mobilis and CM4 medium for C. thermocellum. A
positive control, with pure sugar added, but no feedstock, is used
for comparison. During the incubation, a total of five samples is
taken over a 12 hour period at time 0, 3, 6, 9, and 12 hours and
analyzed for viability (plate counts for Z. mobilis and direct
counts for S. cerevisiae) and ethanol concentration.
Sugar content of the feedstocks is measured using High Performance
Liquid Chromatography (HPLC) equipped with either a Shodex.RTM.
sugar SP0810 or Biorad Aminex.RTM. HPX-87P column. Each of the
feedstocks (approx. 5 g) is mixed with reverse osmosis (RO) water
for 1 hour. The liquid portion of the mixture is removed and
analyzed for glucose, galactose, xylose, mannose, arabinose, and
cellobiose content. The analysis is performed according to National
Bioenergy Center protocol Determination of Structural Carbohydrates
and Lignin in Biomass.
II. Cellulase Compatibility
Feedstocks are tested, in duplicate, with commercially available
Accellerase.RTM. 1000 enzyme complex, which contains a complex of
enzymes that reduces lignocellulosic biomass into fermentable
sugars, at the recommended temperature and concentration in an
Erlenmeyer flask. The flasks are incubated with moderate shaking at
around 200 rpm for 12 hours. During that time, samples are taken
every three hours at time 0, 3, 6, 9, and 12 hours to determine the
concentration of reducing sugars (Hope and Dean, Biotech J., 1974,
144:403) in the liquid portion of the flasks.
Example 20
Alcohol Production Using Irradiation-Sonication Pretreatment
The optimum size for biomass conversion plants is affected by
factors including economies of scale and the type and availability
of biomass used as feedstock. Increasing plant size tends to
increase economies of scale associated with plant processes.
However, increasing plant size also tends to increase the costs
(e.g., transportation costs) per unit of biomass feedstock. Studies
analyzing these factors suggest that the appropriate size for
biomass conversion plants can range from 2000 to 10,000 dried tons
of biomass feedstock per day. The plant described below is sized to
process 2000 tons of dry biomass feedstock per day.
FIG. 41 shows a process schematic of a biomass conversion system
configured to process switchgrass. The feed preparation subsystem
processes raw biomass feedstock to remove foreign objects and
provide consistently sized particles for further processing. The
pretreatment subsystem changes the molecular structure (e.g.,
reduces the average molecular weight and the crystallinity) of the
biomass feedstock by irradiating the biomass feedstock, mixing the
irradiated the biomass feedstock with water to form a slurry, and
applying ultrasonic energy to the slurry. The irradiation and
sonication convert the cellulosic and lignocellulosic components of
the biomass feedstock into fermentable materials. The primary
process subsystem ferments the glucose and other low weight sugars
present after pretreatment to form alcohols.
Example 21
Electron Beam Processing of Table Sugar (Sucrose)
Sucrose was treated with a beam of electrons using a vaulted
Rhodotron.RTM. TT200 continuous wave accelerator delivering 5 MeV
electrons at 80 kW output power. The table below describes the
nominal parameters for the TT200. The nominal doses (in MRad) and
actual doses (in kgy) delivered to the samples are also given
below.
TABLE-US-00013 Rhodotron .RTM. TT 200 Parameters Beam Beam
Produced: Accelerated electrons Beam energy: Nominal (maximum): 10
MeV (+0 keV-250 keV Energy dispersion at 10 Mev: Full width half
maximum (FWHM) 300 keV Beam power at 10 MeV: Guaranteed Operating
Range 1 to 80 kW Power Consumption Stand-by condition (vacuum and
cooling ON): <15 kW At 50 kW beam power: <210 kW At 80 kW
beam power: <260 kW RF System Frequency: 107.5 .+-. 1 MHz
Tetrode type: Thomson TH781 Scanning Horn Nominal Scanning Length
(measured at 25-35 cm 120 cm from window): Scanning Range: From 30%
to 100% of Nominal Scanning Length Nominal Scanning Frequency (at
max. 100 Hz .+-. 5% scanning length): Scanning Uniformity (across
90% of Nominal .+-.5% Scanning Length)
TABLE-US-00014 Dosages Delivered to the Sucrose Samples Total
Dosage (MRad) (Number Associated with Sample ID Delivered Dose
(kgy).sup.1 1 9.9 3 29.0 5 50.4 7 69.2 10 100.0 15 150.3 20 198.3
30 330.9 50 529.0 70 695.9 100 993.6 .sup.1For example, 9.9 kgy was
delivered in 11 seconds at a beam current of 5 mA and a line speed
of 12.9 feet/minute. Cool time between 1 MRad treatments was about
2 minutes.
The solubility of the sucrose samples treated above 30 Mrad was
enhanced, and at or above 30 Mrad, the sucrose appeared visually to
be devoid of crystallinity. Above 70 Mrad, the sucrose was
converted into a solid mass of material. Feed Preparation
The selected design feed rate for the plant is 2,000 dry tons per
day of switchgrass biomass. The design feed is chopped and/or
sheared switchgrass.
Biomass feedstock, in the form of bales of switchgrass, is received
by the plant on truck trailers. As the trucks are received, they
are weighed and unloaded by forklifts. Some bales are sent to
on-site storage while others are taken directly to the conveyors.
From there, the bales are conveyed to an automatic unwrapping
system that cuts away the plastic wrapping and/or net surrounding
the bales. The biomass feedstock is then conveyed past a magnetic
separator to remove tramp metal, after which it is introduced to
shredder-shearer trains where the material is reduced in size.
Finally, the biomass feedstock is conveyed to the pretreatment
subsystem.
In some cases, the switchgrass bales are wrapped with plastic net
to ensure they don't break apart when handled, and may also be
wrapped in plastic film to protect the bale from weather. The bales
are either square or round. The bales are received at the plant
from off-site storage on large truck trailers.
Since switchgrass is only seasonally available, long-term storage
is required to provide feed to the plant year-round. Long-term
storage will likely consist of 400-500 acres of uncovered piled
rows of bales at a location (or multiple locations) reasonably
close to the ethanol plant. On-site short-term storage is provided
equivalent to 72 hours of production at an outside storage area.
Bales and surrounding access ways as well as the transport
conveyors will be on a concrete slab. A concrete slab is used
because of the volume of traffic required to deliver the large
amount of biomass feedstock required. A concrete slab will minimize
the amount of standing water in the storage area, as well as reduce
the biomass feedstock's exposure to dirt. The stored material
provides a short-term supply for weekends, holidays, and when
normal direct delivery of material into the process is
interrupted.
The bales are off-loaded by forklifts and are placed directly onto
bale transport conveyors or in the short-term storage area. Bales
are also reclaimed from short-term storage by forklifts and loaded
onto the bale transport conveyors.
Bales travel to one of two bale unwrapping stations. Unwrapped
bales are broken up using a spreader bar and then discharged onto a
conveyor that passes a magnetic separator to remove metal prior to
shredding. A tramp iron magnet is provided to catch stray magnetic
metal and a scalping screen removes gross oversize and foreign
material ahead of multiple shredder-shearer trains, which reduce
the biomass feedstock to the proper size for pretreatment. The
shredder-shearer trains include shredders and rotary knife cutters.
The shredders reduce the size of the raw biomass feedstock and feed
the resulting material to the rotary knife cutters. The rotary
knife cutters concurrently shear the biomass feedstock and screen
the resulting material.
Three storage silos are provided to limit overall system downtime
due to required maintenance on and/or breakdowns of feed
preparation subsystem equipment. Each silo can hold approximately
55,000 cubic feet of biomass feedstock (.about.3 hours of plant
operation).
Pretreatment
A conveyor belt carries the biomass feedstock from the feed
preparation subsystem 110 to the pretreatment subsystem 114. As
shown in FIG. 42, in the pretreatment subsystem 114, the biomass
feedstock is irradiated using electron beam emitters, mixed with
water to form a slurry, and subjected to the application of
ultrasonic energy. As discussed above, irradiation of the biomass
feedstock changes the molecular structure (e.g., reduces the
average molecular weight and the crystallinity) of the biomass
feedstock. Mixing the irradiated biomass feedstock into a slurry
and applying ultrasonic energy to the slurry further changes the
molecular structure of the biomass feedstock. Application of the
radiation and sonication in sequence may have synergistic effects
in that the combination of techniques appears to achieve greater
changes to the molecular structure (e.g., reduces the average
molecular weight and the crystallinity) than either technique can
efficiently achieve on its own. Without wishing to be bound by
theory, in addition to reducing the polymerization of the biomass
feedstock by breaking intramolecular bonds between segments of
cellulosic and lignocellulosic components of the biomass feedstock,
the irradiation may make the overall physical structure of the
biomass feedstock more brittle. After the brittle biomass feedstock
is mixed into a slurry, the application of ultrasonic energy
further changes the molecular structure (e.g., reduces the average
molecular weight and the crystallinity) and also can reduce the
size of biomass feedstock particles.
Electron Beam Irradiation
The conveyor belt 491 carrying the biomass feedstock into the
pretreatment subsystem distributes the biomass feedstock into
multiple feed streams (e.g., 50 feed streams) each leading to
separate electron beam emitters 492. In this embodiment, the
biomass feedstock is irradiated while it is dry. Each feed stream
is carried on a separate conveyor belt to an associated electron
beam emitter. Each irradiation feed conveyor belt can be
approximately one meter wide. Before reaching the electron beam
emitter, a localized vibration is induced in each conveyor belt to
evenly distribute the dry biomass feedstock over the
cross-sectional width of the conveyor belt.
Electron beam emitter 492 (e.g., electron beam irradiation devices
commercially available from Titan Corporation, San Diego, Calif.)
are configured to apply a 100 kilo-Gray dose of electrons applied
at a power of 300 kW. The electron beam emitters are scanning beam
devices with a sweep width of 1 meter to correspond to the width of
the conveyor belt. In some embodiments, electron beam emitters with
large, fixed beam widths are used. Factors including belt/beam
width, desired dose, biomass feedstock density, and power applied
govern the number of electron beam emitters required for the plant
to process 2,000 tons per day of dry feed.
Sonication
The irradiated biomass feedstock is mixed with water to form a
slurry before ultrasonic energy is applied. There can be a separate
sonication system associated with each electron beam feed stream or
several electron beam streams can be aggregated as feed for a
single sonication system.
In each sonication system, the irradiated biomass feedstock is fed
into a reservoir 1214 through a first intake 1232 and water is fed
into the reservoir 1214 through second intake 1234. Appropriate
valves (manual or automated) control the flow of biomass feedstock
and the flow of water to produce a desired ratio of biomass
feedstock to water (e.g., 10% cellulosic material, weight by
volume). Each reservoir 1214 includes a mixer 1240 to agitate the
contents of volume 1236 and disperse biomass feedstock throughout
the water.
In each sonication system, the slurry is pumped (e.g., using a
recessed impeller vortex pump 1218) from reservoir 1214 to and
through a flow cell 1224 including an ultrasonic transducer 1226.
In some embodiments, pump 1218 is configured to agitate the slurry
1216 such that the mixture of biomass feedstock and water is
substantially uniform at inlet 1220 of the flow cell 1224. For
example, the pump 1218 can agitate the slurry 1216 to create a
turbulent flow that persists throughout the piping between the
first pump and inlet 1220 of flow cell 1224.
Within the flow cell 1224, ultrasonic transducer 1226 transmits
ultrasonic energy into slurry 1216 as the slurry flows through flow
cell 1224. Ultrasonic transducer 1226 converts electrical energy
into high frequency mechanical energy (e.g., ultrasonic energy),
which is then delivered to the slurry through booster 48.
Ultrasonic transducers are commercially available (e.g., from
Hielscher USA, Inc. of Ringwood, N.J.) that are capable of
delivering a continuous power of 16 kilowatts.
The ultrasonic energy traveling through booster 1248 in reactor
volume 1244 creates a series of compressions and rarefactions in
process stream 1216 with an intensity sufficient to create
cavitation in process stream 1216. Cavitation disaggregates
components of the biomass feedstock including, for example,
cellulosic and lignocellulosic material dispersed in process stream
1216 (e.g., slurry). Cavitation also produces free radicals in the
water of process stream 1216 (e.g., slurry). These free radicals
act to further break down the cellulosic material in process stream
1216. In general, about 250 MJ/m.sup.3 of ultrasonic energy is
applied to process stream 1216 containing fragments of poplar
chips. Other levels of ultrasonic energy (between about 5 and about
4000 MJ/m.sup.3, e.g., 10, 25, 50, 100, 250, 500, 750, 1000, 2000,
or 3000) can be applied to other biomass feedstocks After exposure
to ultrasonic energy in reactor volume 1244, process stream 1216
exits flow cell 24 through outlet 1222.
Flow cell 1224 also includes a heat exchanger 1246 in thermal
communication with at least a portion of reactor volume 1244.
Cooling fluid 1248 (e.g., water) flows into heat exchanger 1246 and
absorbs heat generated when process stream 1216 (e.g., slurry) is
sonicated in reactor volume 1244. In some embodiments, the flow of
cooling fluid 1248 into heat exchanger 1246 is controlled to
maintain an approximately constant temperature in reactor volume
1244. In addition or in the alternative, the temperature of cooling
fluid 1248 flowing into heat exchanger 1246 is controlled to
maintain an approximately constant temperature in reactor volume
1244.
The outlet 1242 of flow cell 1224 is arranged near the bottom of
reservoir 1214 to induce a gravity feed of process stream 1216
(e.g., slurry) out of reservoir 1214 towards the inlet of a second
pump 1230 which pumps process stream 1216 (e.g., slurry) towards
the primary process subsystem.
Sonication systems can include a single flow path (as described
above) or multiple parallel flow paths each with an associated
individual sonication unit. Multiple sonication units can also be
arranged to series to increase the amount of sonic energy applied
to the slurry.
Primary Processes
A vacuum rotary drum type filter removes solids from the slurry
before fermentation. Liquid from the filter is pumped cooled prior
to entering the fermentors. Filtered solids are passed to the
post-processing subsystem for further processing.
The fermentation tanks are large, low pressure, stainless steel
vessels with conical bottoms and slow speed agitators. Multiple
first stage fermentation tanks can be arranged in series. The
temperature in the first stage fermentation tanks is controlled to
30 degrees centigrade using external heat exchangers. Yeast is
added to the first stage fermentation tank at the head of each
series of tanks and carries through to the other tanks in the
series.
Second stage fermentation consists of two continuous fermentors in
series. Both fermentors are continuously agitated with slow speed
mechanical mixers. Temperature is controlled with chilled water in
external exchangers with continuous recirculation. Recirculation
pumps are of the progressive cavity type because of the high solids
concentration.
Off gas from the fermentation tanks and fermentors is combined and
washed in a counter-current water column before being vented to the
atmosphere. The off gas is washed to recover ethanol rather than
for air emissions control.
Post-Processing
Distillation
Distillation and molecular sieve adsorption are used to recover
ethanol from the raw fermentation beer and produce 99.5% ethanol.
Distillation is accomplished in two columns--the first, called the
beer column, removes the dissolved CO2 and most of the water, and
the second concentrates the ethanol to a near azeotropic
composition.
All the water from the nearly azeotropic mixture is removed by
vapor phase molecular sieve adsorption. Regeneration of the
adsorption columns requires that an ethanol water mixture be
recycled to distillation for recovery.
Fermentation vents (containing mostly CO2, but also some ethanol)
as well as the beer column vent are scrubbed in a water scrubber,
recovering nearly all of the ethanol. The scrubber effluent is fed
to the first distillation column along with the fermentation
beer.
The bottoms from the first distillation contain all the unconverted
insoluble and dissolved solids. The insoluble solids are dewatered
by a pressure filter and sent to a combustor. The liquid from the
pressure filter that is not recycled is concentrated in a multiple
effect evaporator using waste heat from the distillation. The
concentrated syrup from the evaporator is mixed with the solids
being sent to the combustor, and the evaporated condensate is used
as relatively clean recycle water to the process.
Because the amount of stillage water that can be recycled is
limited, an evaporator is included in the process. The total amount
of the water from the pressure filter that is directly recycled is
set at 25%. Organic salts like ammonium acetate or lactate, steep
liquor components not utilized by the organism, or inorganic
compounds in the biomass end up in this stream. Recycling too much
of this material can result in levels of ionic strength and osmotic
pressures that can be detrimental to the fermenting organism's
efficiency. For the water that is not recycled, the evaporator
concentrates the dissolved solids into a syrup that can be sent to
the combustor, minimizing the load to wastewater treatment.
Wastewater Treatment
The wastewater treatment section treats process water for reuse to
reduce plant makeup water requirements. Wastewater is initially
screened to remove large particles, which are collected in a hopper
and sent to a landfill. Screening is followed by anaerobic
digestion and aerobic digestion to digest organic matter in the
stream. Anaerobic digestion produces a biogas stream that is rich
in methane that is fed to the combustor. Aerobic digestion produces
a relatively clean water stream for reuse in the process as well as
a sludge that is primarily composed of cell mass. The sludge is
also burned in the combustor. This screening/anaerobic
digestion/aerobic digestion scheme is standard within the current
ethanol industry and facilities in the 1-5 million gallons per day
range can be obtained as "off-the-shelf" units from vendors.
Combustor, Boiler, and Turbogenerator
The purpose of the combustor, boiler, and turbogenerator subsystem
is to burn various by-product streams for steam and electricity
generation. For example, some lignin, cellulose, and hemicellulose
remains unconverted through the pretreatment and primary processes.
The majority of wastewater from the process is concentrated to a
syrup high in soluble solids. Anaerobic digestion of the remaining
wastewater produces a biogas high in methane. Aerobic digestion
produces a small amount of waste biomass (sludge). Burning these
by-product streams to generate steam and electricity allows the
plant to be self sufficient in energy, reduces solid waste disposal
costs, and generates additional revenue through sales of excess
electricity.
Three primary fuel streams (post-distillate solids, biogas, and
evaporator syrup) are fed to a circulating fluidized bed combustor.
The small amount of waste biomass (sludge) from wastewater
treatment is also sent to the combustor. A fan moves air into the
combustion chamber. Treated water enters the heat exchanger circuit
in the combustor and is evaporated and superheated to 510.degree.
C. (950.degree. F.) and 86 atm (1265 psia) steam. Flue gas from the
combustor preheats the entering combustion air then enters a
baghouse to remove particulates, which are landfilled. The gas is
exhausted through a stack.
A multistage turbine and generator are used to generate
electricity. Steam is extracted from the turbine at three different
conditions for injection into the pretreatment reactor and heat
exchange in distillation and evaporation. The remaining steam is
condensed with cooling water and returned to the boiler feedwater
system along with condensate from the various heat exchangers in
the process. Treated well water is used as makeup to replace steam
used in direct injection.
Other Embodiments
A number of embodiments of the invention have been described.
Nevertheless, it will be understood that various modifications may
be made without departing from the spirit and scope of the
invention. Accordingly, other embodiments are within the scope of
the following claims.
* * * * *